Editing Roman calendar

{{short description|Calendar used by the Roman Kingdom and Roman Republic}}
{{redirect|Roman month|the unit of military contribution in the Holy Roman Empire|Roman Month}}
{{for|the Catholic liturgical calendar|General Roman Calendar}}
{{page numbers needed |date=February 2025}}
{{Use mdy dates|date=December 2023}}
[[File:Museo del Teatro Romano de Caesaraugusta.43.jpg|thumb|300px|alt=Museum of the Roman Theater of Caesaraugusta in Zaragoza, Spain|A reproduction of the ''{{lang|la|[[Fasti Antiates Maiores]]}}'', a painted wall-calendar from the late Roman Republic]]
[[File:Roman-calendar.png|thumb|300px|Another reproduction of the fragmentary ''{{lang|la|Fasti Antiates Maiores}}'' {{nowrap|({{circa| 60}} BC)}}, with the seventh and eighth months still named [[Quintilis]] ("QVI") and [[Sextilis]] ("SEX") and an [[intercalary month]] ("INTER") in the far right-hand column]]

The '''Roman calendar''' was the [[calendar]] used by the [[Roman Kingdom]] and [[Roman Republic]]. Although the term is primarily used for Rome's pre-Julian calendars, it is often used inclusively of the [[Julian calendar]] established by [[Julius Caesar]] in 46&nbsp;BC.{{efn|The term does not include the [[Alexandrian calendar]] of [[Roman Egypt]], which continued the unique months of that land's [[Egyptian calendar|former calendar]]; the [[Byzantine calendar]] of the [[Byzantine Empire|later Roman Empire]], which usually dated the Roman months in the simple count of the [[ancient Greek calendar]]s; and the [[Gregorian calendar]], which refined the Julian system to bring it into still closer alignment with the [[tropical year]].}}

According to most Roman accounts, [[#Romulus|their original calendar]] was established by their [[Roman legend|legendary]] [[list of kings of Rome|first king]] [[Romulus]]. It consisted of ten [[month]]s, beginning in spring with March and leaving winter as an unassigned span of days before the next year. These months each had 30 or 31 [[day]]s and ran for 38 [[nundinal cycles]], each forming a kind of eight-day [[week]]{{mdash}}nine days [[inclusive counting|counted inclusively in the Roman manner]]{{mdash}}and ending with religious rituals and a [[Roman commerce|public market]]. This fixed calendar bore traces of its origin as an [[observational calendar|observational]] [[lunar calendar|lunar one]]. In particular, the most important days of each month{{mdash}}its [[kalends]], [[nones (calendar)|nones]], and [[ides (calendar)|ides]]{{mdash}}seem to have derived from the [[new moon]], the [[first-quarter moon]], and the [[full moon]] respectively. To a late date, the [[College of Pontiffs]] formally proclaimed each of these days on the [[Capitoline Hill]] and Roman dating counted down inclusively towards the next such day in any month. (For example, the year-end festival of [[Terminalia (festival)|Terminalia]] on 23{{spaces}}February was called {{lang|la|VII. {{linktext|Kal.}} {{linktext|Mart.}}}}, the 6th day before the March kalends.)

Romulus's successor [[Numa Pompilius]] was then usually credited with a [[#Numa|revised calendar]] that divided winter between the two months of [[Ianuarius|January]] and [[Februarius|February]], shortened most other months accordingly, and brought everything into rough alignment with the [[solar year]] by some system of [[intercalation (timekeeping)|intercalation]]. This is a typical element of [[lunisolar calendar]]s and was necessary to keep the [[ancient Roman religion|Roman religious]] [[Roman festivals|festivals]] and other activities in their proper [[season]]s.

Modern historians dispute various points of this account. It is possible the original calendar was agriculturally based, observational of the seasons and stars rather than of the moon, with ten months of varying length filling the entire year. If this ever existed, it would have changed to the lunisolar system later credited to Numa during the kingdom or [[early Republic]] under the influence of the [[Etruscan culture|Etruscans]] and of [[Pythagoreans|Pythagorean]] [[Magna Graeca|Southern Italian Greeks]]. After the [[overthrow of the Roman monarchy|establishment of the Republic]], [[year]]s [[calendar epoch|began to be dated]] by [[Roman consul|consulships]] but the calendar and its rituals were otherwise very conservatively maintained until the [[Late Republic]]. Even when the nundinal cycles had completely departed from correlation with the moon's phases, a [[pontifex minor|pontiff]] was obliged to meet the [[rex sacrorum|sacred king]], to claim that he had observed the new moon, and to offer a sacrifice to [[Juno (goddess)|Juno]] to solemnize each kalends.

It is clear that, for a variety of reasons, the intercalation necessary for the system's accuracy was not always observed. Astronomical events recorded in [[Livy]] show the civil calendar had varied from the solar year by an entire season in {{nowrap|190 BC}} and was still two months off in {{nowrap|168 BC}}. By the {{nowrap|191 BC}} {{lang|la|[[Lex Acilia de Intercalando|Lex Acilia]]}} or before, control of intercalation was given to the [[pontifex maximus]] but{{mdash}}as these were often [[politics in ancient Rome|active political leaders]] like [[Julius Caesar|Caesar]]{{mdash}}political considerations continued to interfere with its regular application.

Victorious in civil war, Caesar [[Julian reform|reformed the calendar]] in 46 BC, coincidentally making the year of his third consulship last for 446{{spaces}}days. This new Julian calendar was an entirely [[solar calendar|solar one]], influenced by the [[Egyptian calendar]]. In order to avoid interfering with Rome's religious ceremonies, the reform distributed the unassigned days among the months (towards their ends) and did not adjust any nones or ides, even in months which came to have 31{{spaces}}days. The Julian calendar was designed to have a single [[leap day]] every fourth year by repeating February 24{{efn|Two days in a row were given the same date. [[Bissextus|This practice]] continued well into the sixteenth century.}} (a doubled {{lang|la|VI. Kal. Mart.}} or {{lang|la|ante diem bis sextum Kalendas Martias}}) but, following [[Assassination of Caesar|Caesar's assassination]], the priests mistakenly added the [[bissextile]] ({{lang|la|bis sextum}}) leap day every three years due to their inclusive counting. In order to bring the calendar back to its proper place, Augustus was obliged to suspend intercalation for one or two decades.

At 365.25 days, the Julian calendar remained slightly longer than the solar year (365.24 days).<!--Two decimal places is adequately precise for the lead. --> By the 16th century, the [[date of Easter]] had shifted so far away from the [[March equinox|vernal equinox]] that [[Pope Gregory XIII|Pope Gregory&nbsp;XIII]] ordered a further correction to the calendar method, resulting in the establishment of the modern [[Gregorian calendar]].

==History==
[[File:Fasti Praenestini Massimo n1.jpg|thumb|right|250px|The remains of the ''{{lang|la|[[Fasti Praenestini]]}}'', containing the months of January, March, April, and December and a portion of February.{{sfnp|''Enc. Brit.''|1911|p=193}}]]
{{anchor|Lunar|Lunar calendar|Prehistory|Prehistoric}}

===Prehistoric calendar===
The original Roman [[calendar]] is usually believed to have been an [[observational calendar|observational]] [[lunar calendar]]{{sfnp|Mommsen & al.|1864|p=[https://archive.org/stream/historyrome00dickgoog#page/n242/mode/2up 216]}} whose months ended and began from the [[new moon]].{{sfnp|Michels|1949|pp=323–324}}{{sfnp|Grout|2023}} Because a [[lunar phase|lunar cycle]] is about 29.5 days long, such months would have varied between {{nowrap|29 and 30 days}}.<ref name=mommy/> Twelve such months would have fallen {{nowrap|10 or 11 days}} short of the [[solar year]] and, without adjustment, such a year would have quickly rotated out of alignment with the seasons<ref name=mommy/> in the manner of the [[Islamic calendar]]. Given the seasonal aspects of the calendar and its associated [[ancient Roman religion|religious]] [[ancient Roman festivals|festivals]], this was presumably avoided through some form of arbitrary curtailment or intercalation<ref name=mommy/> or through the suspension of the calendar during winter.
Against this, [[Agnes Kirsopp Lake Michels|Michels]] has argued that the early calendars used by Rome and its neighbors were more probably observational of seasonal markers in nature (the [[leafing]] of trees), animal behavior (the [[bird migration|migration]] of birds), and the [[agriculture in ancient Rome|agricultural cycle]] (the ripening of [[Agriculture in ancient Rome#Grains|grain]]) combined with observation of [[star]]s in the [[night sky]].{{sfnp|Michels|1949|p=330}} She considers that this more sensibly accounts for later legends of [[Romulus]]'s [[#Romulus|decimal year]] and the great irregularity in Italian month lengths recorded in [[Censorinus]].{{sfnp|Michels|1949|p=330}}<ref>[[Censorinus]], ''[[De Die Natali|The Natal Day]]'', [https://elfinspell.com/ClassicalTexts/Maude/Censorinus/DeDieNatale-Part2.html#topref94 Ch. XXII].</ref> Roman works on agriculture including those of [[Cato the Elder|Cato]],<ref>[[Cato the Elder|Cato]], ''[[De Agri Cultura|On Agriculture]]''.</ref> [[Varro]],<ref>[[Varro]], ''[[Res Rusticae|Farming]]''.</ref> [[Vergil]],<ref>[[Vergil]], ''[[Georgics]]''.</ref> [[Columella]],<ref>[[Columella]], ''[[De Re Rustica (Columella)|On Farming]]''.</ref> and [[Pliny the Elder|Pliny]]<ref>[[Pliny the Elder|Pliny]], ''[[Natural History (Pliny)|Natural History]]''.</ref> invariably date their practices based on suitable conditions or upon the [[rising of stars]], with only occasional supplementary mention of the [[#Republican calendar|civil calendar]] of their times{{sfnp|Michels|1949|p=330}} until the 4th or 5th century author [[Rutilius Taurus Aemilianus Palladius|Palladius]].<ref>[[Rutilius Taurus Aemilianus Palladius|Palladius]], ''[[De Re Rustica (Palladius)|On Farming]]''.</ref> [[Augury]], formal Roman [[ornithomancy]], continued to be the focus of a [[augur|prestigious dedicated priesthood]] until at least the end of the 4th century.{{sfnp|Wissowa|1896}} Although most Roman festivals in the historical record were closely tied to the [[nundinal cycle]] of the [[#Numa|later calendar]],{{sfnp|Michels|1949|p=322}} there remained several [[moveable feasts]] ({{lang|la|[[feriae conceptivae]]}}, "proclaimed festivals") like the [[Sementivae]] that were dependent on local conditions.{{sfnp|Michels|1949|p=331}} Michels suggests this was the original state of all ancient festivals, marking divisions between the seasons and occasions within them.{{sfnp|Michels|1949|p=331}}

{{anchor|Romulus|Romulan calendar|Calendar of Romulus}}

===Legendary 10-month calendar===
The Romans themselves usually described their first organized year as one with ten fixed months,{{sfn|Macrobius|loc=Book I, Ch. 12, §3}}{{sfnp|Kaster|2011|p=137}} a decimal division fitting general Roman practice.{{sfnp|Mommsen & al.|1864|p=[https://archive.org/stream/historyrome00dickgoog#page/n242/mode/2up 217]}} There were four months of "31" days{{sfn|Macrobius|loc=Book I, Ch. 12, §3}}{{mdash}}March, May, Quintilis, and October{{mdash}}called "full months" ({{lang|la|[[wikt:pleni menses#Latin|pleni menses]]}}) and six months of "30" days{{sfn|Macrobius|loc=Book I, Ch. 12, §3}}{{mdash}}April, June, Sextilis, September, November, and December{{mdash}}called "hollow months" (''{{lang|la|[[wikt:cavi menses#Latin|cavi menses]]}}'').<ref>[[Censorinus]], [[Macrobius]], and [[Gaius Julius Solinus|Solinus]], cited in {{harvp|Key|1875}}</ref><ref name=mommy>{{harvp|Mommsen & al.|1864|p=[https://archive.org/stream/historyrome00dickgoog#page/n244/mode/2up 218]}}.</ref> These "304"&nbsp;days made up exactly 38&nbsp;[[nundinal cycle]]s. The months were kept in alignment with the moon, however, by counting the [[new moon]] as the last day of the first month and simultaneously the first day of the next month.{{sfnp|Grout|2023}} The system is usually said to have left the remaining two to three months of the year as an unorganized "winter", since they were irrelevant to the farming cycle.{{sfnp|Grout|2023}} [[Macrobius]] claims the 10-month calendar was fixed and allowed to shift until the summer months were completely misplaced, at which time additional days belonging to no month were simply inserted into the calendar until it seemed things were restored to their proper place.{{sfn|Macrobius|loc=Book I, Ch. 12, §39}}{{sfnp|Kaster|2011|p=155}} [[Gaius Licinius Macer|Licinius Macer]]'s lost history apparently similarly stated that even the earliest Roman calendar employed intercalation.<ref name=censibility>[[Censorinus]], ''[[De Die Natali|The Natal Day]]'', [https://elfinspell.com/ClassicalTexts/Maude/Censorinus/DeDieNatale-Part2.html Ch. XX].</ref>{{sfn|Macrobius|loc=Book I, Ch. 13, §20}}{{sfnp|Kaster|2011|p=165}}

Later Roman writers usually credited this calendar to [[Romulus]],{{sfn|Macrobius|loc=Book I, Ch. 12, §§5 & 38}}{{sfnp|Kaster|2011|pp=137 & 155}} their [[Roman legend|legendary]] [[Kings of Rome|first king]] and [[culture hero]], although this was common with other practices and traditions whose origin had been lost to them. [[Censorinus]] considered him to have borrowed the system from [[Alba Longa]],<ref name=censibility/> his supposed birthplace. Some scholars doubt the existence of this calendar at all, as it is only attested in late Republican and Imperial sources and supported only by the misplaced names of the months from September to December.<ref name=rupparena>{{harvp|Rüpke|2011|p=[https://books.google.com/books?id=pThna2LDwDsC&pg=PA23 23]}}.</ref> [[Jörg Rüpke|Rüpke]] also finds the coincidence of the length of the supposed "Romulan" year with the length of the first ten months of the Julian calendar to indicate that it is an {{lang|la|[[a priori]]}} interpretation by late Republican writers.<ref name=rupparena/>

{| class="wikitable plainrowheaders" style="margin:1em auto;"
|+ Calendar of Romulus
|-
! scope="col" | English
! scope="col" | Latin
! scope="col" | Meaning
! scope="col" | Length in days{{sfn|Macrobius|loc=Book I, Ch. 12, §3}}{{sfnp|Kaster|2011|p=137}}
|-
| [[March]] || [[Martius (month)|Mensis Martius]] || Month of [[Mars (mythology)|Mars]]
| style="font-weight: bold;"| 31
|-
| [[April]] || [[Mensis Aprilis]] || Month of Apru ([[Aphrodite]])<ref>{{cite web | title=April | website=Dictionary.com Unabridged | publisher=Randomhouse Inc. | url=http://www.dictionary.com/browse/april | access-date=January 9, 2018}}</ref>
| 30
|-
| [[May]] || [[Mensis Maius]] || Month of [[Maia (mythology)|Maia]]<ref>{{cite web | title=May | website=Dictionary.com Unabridged | publisher=Randomhouse Inc. | url=http://www.dictionary.com/browse/may | access-date=January 9, 2018}}</ref>
| style="font-weight: bold;" | 31
|-
| [[June]] || [[Iunius (month)|Mensis Iunius]] || Month of [[Juno (mythology)|Juno]]
| 30 
|-
| [[July]] || [[Mensis Quintilis]]<br>Mensis Quinctilis{{sfnp|Blackburn & al.|1999|p=669}} || Fifth Month
| style="font-weight: bold;" | 31
|-
| [[August]] || [[Mensis Sextilis]] || Sixth Month
| 30
|-
| [[September]] || [[September (Roman month)|Mensis September]] || Seventh Month
| 30
|-
| [[October]] || [[October (Roman month)|Mensis October]] || Eighth Month
| style="font-weight: bold;" | 31
|-
| [[November]] || [[November (Roman month)|Mensis November]] || Ninth Month
| 30
|-
| [[December]] || [[December (Roman month)|Mensis December]] || Tenth Month
| 30
|- 
! scope="row" colspan="3" style="text-align: right;" | Length of the year:
! style="text-align: left;" | 304
|}

Other traditions existed alongside this one, however. [[Plutarch]]'s ''[[Parallel Lives]]'' recounts that [[Romulus]]'s calendar had been solar but adhered to the general principle that the year should last for 360&nbsp;days. Months were employed secondarily and haphazardly, with some counted as 20&nbsp;days and others as 35 or more.<ref name=gossipgirl/><ref name=worchestershire/> Plutarch records that while one tradition is that [[Numa Pompilius|Numa]] added two new months to a ten-month calendar, another version is that January and February were originally the last two months of the year and Numa just moved them to the start of the year, so that January (named after a peaceful ruler called [[Janus]]) would come before March (which was named for Mars, the god of war).<ref>{{harvp|Plutarch|loc=''Life of Numa'' section XIX}}</ref>

Rome's 8-day week, the [[nundinal cycle]], was shared with the [[Etruscans]], who used it as the schedule of royal audiences. It was presumably a part of the early calendar and was credited in [[Roman legend]] variously to [[Romulus]] and [[Servius Tullius]].

{{anchor|Numa|Calendar of Numa|Numan reform}}

===Republican calendar===
The attested calendar of the [[Roman Republic]] was quite different. It had twelve months, already including [[Ianuarius|January]] and [[Februarius|February]] during the winter.

According to Livy, it was Numa Pompilius, the second king of Rome {{nowrap|(715–673 BC),}} who divided the year into twelve lunar months (History of Rome, I.19). Fifty days, says Censorinus, were added to the calendar and a day taken from each month of thirty days to provide for the two winter months: Januarius (January) and Februarius (February), both of which had 28 days (The Natal Day, XX). This was a lunar year of 354 days but, because of the Roman superstition about even numbers, an additional day was added to January to make the calendar 355 days long. Auspiciously, each month now had an odd number of days: Martius (March), Maius (May), Quinctilis (July), and October continued to have 31; the other months, 29, except for February, which had 28 days. Considered unlucky, it was devoted to rites of purification (februa) and expiation appropriate to the last month of the year. (Although these legendary beginnings attest to the venerability of the lunar calendar of the Roman Republic, its historical origin probably was the publication of a revised calendar by the Decemviri in {{nowrap|450 BC}} as part of the [[Twelve Tables]], Rome's first code of law.)
{{sfnp|Grout|2023}}

The inequality between the lunar year of 355 days and the [[tropical year]] of 365.25 days led to a shortfall over four years of (10.25 × 4) = 41 days.<ref name=mommy/> Theoretically, 22 days were interpolated into the calendar in the second year of the four-year cycle and 23 days in the fourth.<ref name=mommy/> This produced an excess of four days over the four years in line with the normal one day excess over one year. The method of correction was to truncate February by five days and follow it with the intercalary month which thus commenced (normally) on the day after February 23 and had either 27 or 28 days. February 23 was the [[Terminalia (festival)|Terminalia]] and in a normal year it was ''{{lang|la|a.d. VII Kal. Mart.}}'' Thus the dates of the festivals of the last five days of February were preserved<ref name=rupkenuma1>{{harvp|Rüpke|2011|p=[https://books.google.com/books?id=pThna2LDwDsC&pg=PA40 40]}}</ref> on account of them being actually named and counted inclusively in days before the [[kalends]] of March; they were traditionally part of the celebration for the new year. There was occasionally a delay of one day (a {{lang|la|dies intercalaris}} being inserted between February 23 and the start of the {{lang|la|mensis intercalaris}}) for the purpose of avoiding a clash between a particular festival and a particular day of the week (see {{slink|Hebrew calendar|Rosh Hashanah postponement rules}} for another example).  The Roman superstitions concerning the numbering and order of the months seem to have arisen from [[Pythagoreans|Pythagorean]] superstitions concerning the luckiness of [[odd number]]s.<ref name=momma>{{harvp|Mommsen & al.|1864|p=[https://archive.org/stream/historyrome00dickgoog#page/n244/mode/2up 219]}}.</ref>

These Pythagorean-based changes to the Roman calendar were generally credited by the Romans to [[Numa Pompilius]],{{sfnp|Grout|2023}} [[Romulus]]'s successor and the second of [[kings of Rome|Rome's seven kings]], as were the two new months of the calendar.{{sfn|Macrobius|loc=Book I, Ch. 12, §34}}{{sfnp|Kaster|2011|p=153}}{{efn|[[Plutarch]] reports this tradition while claiming that the months had more probably predated or originated with Romulus.<ref name=gossipgirl/><ref name=worchestershire/>}} Most sources thought he had established intercalation with the rest of his calendar.{{citation needed|date=March 2017}} Although [[Livy]]'s Numa instituted a lunar calendar, the author claimed the king had instituted a 19-year system of intercalation equivalent to the [[Metonic cycle]]{{sfnp|Livy|loc=Book I, Ch. 19, §6}} centuries before its development by [[Babylonian astronomers|Babylonian]] and [[Ancient Greek astronomy|Greek astronomers]].{{efn|This equivalence was first described by [[Temple Stanyan|Stanyan]] in his history of ancient Greece.{{sfnp|Stanyan|1707|p=[https://archive.org/stream/grecianhistoryf00stangoog#page/n373/mode/2up 330]}}}} [[Plutarch]]'s account claims he ended the former chaos of the calendar by employing 12{{spaces}}months totalling 354{{spaces}}days—the length of the [[synodic month|lunar]] and [[ancient Greek calendars|Greek years]]—and a biennial intercalary month of 22{{spaces}}days called [[Mercedonius]].<ref name=gossipgirl/><ref name=worchestershire/>

According to Livy's [[Periochae]], the beginning of the consular year changed from March to 1{{spaces}}January in 153{{spaces}}BC to respond to a rebellion in Hispania.<ref>Livy, ''Periochae'', [https://www.livius.org/sources/content/livy/livy-periochae-46-50/#47.1 47.13 and 47.14]: "[47.13] In the five hundred and ninety-eighth year after the founding of the city, the consuls began to enter upon their office on 1{{spaces}}January. [47.14] The cause of this change in the date of the elections was a rebellion in Hispania."</ref> Plutarch believed Numa was responsible for placing January and February first in the calendar;<ref name=gossipgirl/><ref name=worchestershire/> [[Ovid]] states January began as the first month and February the last, with its present order owing to the [[Decemvirs]].{{sfnp|Ovid|loc=Book II}}{{sfnp|Kline|2004|loc=[https://www.poetryintranslation.com/PITBR/Latin/OvidFastiBkTwo.php#anchor_Toc69367683 Book II, Introduction]}} [[W. Warde Fowler]] believed the [[Ancient Roman religion|Roman priests]] continued to treat January and February as the last months of the calendar throughout the Republican period.{{sfnp|Fowler|1899|p=5}}

{|class="wikitable" style="margin:.5em auto;line-height:1.4"
|+ Roman Republican calendar ({{circa|700 BC}} or {{circa|450 BC}} – 46 BC)
|-
!scope="col" colspan="3" rowspan="2"| English
!scope="col" colspan="3" rowspan="2"| Latin
!scope="col" colspan="2" rowspan="2"| Meaning
!scope="col" colspan="4"| Length in days{{sfn|Macrobius}}{{sfnp|Kaster|2011}}<ref name=gossipgirl>{{harvp|Plutarch|loc=''Life of Numa'' section XVIII}}.</ref><ref name=worchestershire>{{harvp|Perrin|1914|pp=[https://penelope.uchicago.edu/Thayer/E/Roman/Texts/Plutarch/Lives/Numa*.html#Romulan_year 368 ff]}}.</ref>
|-
!scope="col" style="line-height:1.25"| 1st<br /> year<br /> <small>([[Common year|cmn.]])</small>
!scope="col" style="line-height:1.25"| 2nd<br /> year<br /> <small>([[Leap year|leap]])</small>
!scope="col" style="line-height:1.25"| 3rd<br /> year<br /> <small>(cmn.)</small>
!scope="col" style="line-height:1.25"| 4th<br /> year<br /> <small>(leap)</small>
|-style="background:#CFC"
|style="text-align:right"| 1. ||colspan="2"| January
|style="text-align:right"| I. ||colspan="2"| [[Mensis Ianuarius]]
|colspan="2"| Month of [[Janus]]
|style="text-align:center"| 29
|style="text-align:center"| 29
|style="text-align:center"| 29
|style="text-align:center"| 29
|-style="background:#CFC"
|rowspan="2" style="text-align:right"| 2. ||colspan="2"| February
|rowspan="2" style="text-align:right"| II. ||colspan="2"| [[Mensis Februarius]]
|colspan="2"| Month of the [[Lupercalia|Februa]]
|style="text-align:center"| 28
|style="text-align:center"| 23
|style="text-align:center"| 28
|style="text-align:center"| 23
|-style="background:#CFC"
|style="border-top:hidden;border-bottom:hidden;width:1em"| &nbsp; || Intercalary Month
|style="border-top:hidden;border-bottom:hidden;width:1em"| &nbsp; || Intercalaris Mensis ([[Mercedonius]])
|style="border-top:hidden;border-bottom:hidden;width:1em"| &nbsp; || Month of Wages
|style="border-top:hidden;text-align:center"| &nbsp;
|style="text-align:center"|'''27'''
|style="border-top:hidden;text-align:center"| &nbsp;
|style="text-align:center"|'''28'''
|-
|style="text-align:right"| 3. ||colspan="2"| March
|style="text-align:right"| III. ||colspan="2"| [[Martius (month)|Mensis Martius]]
|colspan="2"| Month of [[Mars (mythology)|Mars]]
|style="text-align:center"| 31
|style="text-align:center"| 31
|style="text-align:center"| 31
|style="text-align:center"| 31
|-
|style="text-align:right"| 4. ||colspan="2"| April
|style="text-align:right"| IV. ||colspan="2"| [[Mensis Aprilis]]
|colspan="2"| Month of [[Aphrodite]] – from which the [[Etruscan language|Etruscan]] Apru might have been derived
|style="text-align:center"| 29
|style="text-align:center"| 29
|style="text-align:center"| 29
|style="text-align:center"| 29
|-
|style="text-align:right"| 5. ||colspan="2"| May
|style="text-align:right"| V. ||colspan="2"| [[Mensis Maius]]
|colspan="2"| Month of [[Maia]]
|style="text-align:center"| 31
|style="text-align:center"| 31
|style="text-align:center"| 31
|style="text-align:center"| 31
|-
|style="text-align:right"| 6. ||colspan="2"| June
|style="text-align:right"| VI. ||colspan="2"| [[Iunius (month)|Mensis Iunius]]
|colspan="2"| Month of [[Juno (mythology)|Juno]]
|style="text-align:center"| 29
|style="text-align:center"| 29
|style="text-align:center"| 29
|style="text-align:center"| 29
|-
|style="text-align:right"| 7. ||colspan="2"| July
|style="text-align:right"| VII. ||colspan="2"| [[Mensis Quintilis]]
|colspan="2"| Fifth Month (from the earlier calendar starting in March)
|style="text-align:center"| 31
|style="text-align:center"| 31
|style="text-align:center"| 31
|style="text-align:center"| 31
|-
|style="text-align:right"| 8. ||colspan="2"| August
|style="text-align:right"| VIII. ||colspan="2"| [[Mensis Sextilis]]
|colspan="2"| Sixth Month
|style="text-align:center"| 29
|style="text-align:center"| 29
|style="text-align:center"| 29
|style="text-align:center"| 29
|-
|style="text-align:right"| 9. ||colspan="2"| September
|style="text-align:right"| IX. ||colspan="2"| [[September (Roman month)|Mensis September]]
|colspan="2"| Seventh Month
|style="text-align:center"| 29
|style="text-align:center"| 29
|style="text-align:center"| 29
|style="text-align:center"| 29
|-
|style="text-align:right"| 10. ||colspan="2"| October
|style="text-align:right"| X. ||colspan="2"| [[October (Roman month)|Mensis October]]
|colspan="2"| Eighth Month
|style="text-align:center"| 31
|style="text-align:center"| 31
|style="text-align:center"| 31
|style="text-align:center"| 31
|-
|style="text-align:right"| 11. ||colspan="2"| November
|style="text-align:right"| XI. ||colspan="2"| [[November (Roman month)|Mensis November]]
|colspan="2"| Ninth Month
|style="text-align:center"| 29
|style="text-align:center"| 29
|style="text-align:center"| 29
|style="text-align:center"| 29
|-
|style="text-align:right"| 12. ||colspan="2"| December
|style="text-align:right"| XII. ||colspan="2"| [[December (Roman month)|Mensis December]]
|colspan="2"| Tenth Month
|style="text-align:center"| 29
|style="text-align:center"| 29
|style="text-align:center"| 29
|style="text-align:center"| 29
|-
!scope="row" colspan="8" style="text-align:right"| Whole year:
|style="text-align:center"| 355
|style="text-align:center"| 377
|style="text-align:center"| 355
|style="text-align:center"| 378
|}

According to the later writers Censorinus and Macrobius, to correct the mismatch of the correspondence between months and seasons due to the excess of one day of the Roman average year over the tropical year, the insertion of the intercalary month was modified according to the scheme: common year (355 days), leap year with 23-day February followed by 27-day Mercedonius (377 days), common year, leap year with 23-day February followed by 28-day Mercedonius (378 days), and so on for the first 16 years of a 24-year cycle. In the last 8 years, the intercalation took place with the month of Mercedonius only 27 days, except the last intercalation which did not happen. Hence, there would be a typical common year followed by a leap year of 377 days for the next 6 years and the remaining 2 years would sequentially be common years. The result of this twenty-four-year pattern was of great precision for the time: 365.25 days, as shown by the following calculation:

<math>\frac{355\times 13+377\times 7+378\times 4}{24}=\frac{8,766}{24}=365\tfrac{1}{4}</math>

The consuls' terms of office were not always a modern calendar year, but ordinary consuls were elected or appointed annually. The traditional [[list of Roman consuls]] used by the Romans to date their years began in 509 BC.<ref name=matlock>{{harvp|Mathieson|2003|p=[https://books.google.com/books?id=krcp3GU2MssC&pg=PA14 14]}}.</ref>

{{anchor|Gnaeus Flavius}}

===Flavian reform===
[[Gnaeus Flavius (jurist)|Gnaeus Flavius]], a secretary (''scriba'') to censor [[Appius Claudius Caecus|App. Claudius Caecus]], introduced a series of reforms in 304 BC.{{sfnp|Michels|1949|p=340}} Their exact nature is uncertain, although he is thought to have begun the custom of publishing the calendar in advance of the month, depriving the priests of some of their power but allowing for a more consistent calendar for official business.{{sfnp|Lanfranchi|2013}}

{{anchor|Julius Caesar|Caesar|Julian calendar}}

===Julian reform===
{{main|Julian calendar}}
[[Julius Caesar]], following his [[Battle of Pharsalia|victory]] in [[Caesar's Civil War|his civil war]] and in his role as ''[[pontifex maximus]]'', ordered a [[Julian reform|reformation of the calendar]] in 46 BC. This was undertaken by a group of scholars apparently including the [[Alexandria]]n [[Sosigenes of Alexandria|Sosigenes]]{{sfnp|Pliny|loc=Book XVIII, Ch. 211}} and the Roman M. Flavius.{{sfn|Macrobius|loc=Book I, Ch. 14, §2}}{{sfnp|Kaster|2011}} Its main lines involved the insertion of ten additional days throughout the calendar and regular intercalation of a single [[leap day]] every fourth year to bring the Roman calendar into close agreement with the solar year. The year 46 BC was the last of the old system and included three intercalary months, the first inserted in February and two more—''{{lang|la|Intercalaris Prior}}'' and ''{{lang|la|Posterior}}''—before the kalends of December.

===Later reforms===
{{main|Byzantine calendar}}
After [[Assassination of Julius Caesar|Caesar's assassination]], [[Mark Antony]] had Caesar's birth month Quintilis renamed [[July (month)|July]] (''{{lang|la|Iulius}}'') in his honor. After Antony's [[Battle of Actium|defeat at Actium]], [[Augustus]] assumed control of Rome and, finding the priests had (owing to their inclusive counting) been intercalating every third year instead of every fourth, suspended the addition of leap days to the calendar for one or two decades until its proper position had been restored. See [[Julian calendar#Leap year error|Julian calendar: Leap year error]]. In 8 BC, the [[plebiscite]] ''Lex Pacuvia de Mense Augusto'' renamed Sextilis [[August (month)|August]] (''{{lang|la|Augustus}}'') in his honor.{{sfnp|Rotondi|1912|p=441}}{{sfn|Macrobius|loc=Book I, Ch. 12}}{{sfnp|Kaster|2011}}{{efn|There are some documents which state the month had been renamed as early as 26 or 23 BC, but the date of the Lex Pacuvia is certain.}}

In large part, this calendar continued unchanged under the [[Roman Empire]]. ([[Roman Egypt|Egypt]]ians used the related [[Alexandrian calendar]], which Augustus had adapted from [[Egyptian calendar|their wandering ancient calendar]] to maintain its alignment with Rome's.) A few emperors altered the names of the months after themselves or their family, but such changes were abandoned by their successors. [[Diocletian]] began the 15-year [[indiction]] cycles beginning from the AD 297 census;<ref name=matlock/> these became the required format for official dating under [[Justinian I|Justinian]]. [[Constantine the Great|Constantine]] formally established the 7-day [[week]] by making [[Sunday]] an official holiday in 321.{{Citation needed|date=November 2019}} Consular dating became obsolete following the abandonment of appointing nonimperial consuls in AD 541.<ref name=matlock/> The Roman method of numbering the days of the month never became widespread in the Hellenized eastern provinces and was eventually abandoned by the [[Byzantine Empire]] in [[Byzantine calendar|its calendar]].

{{anchor|Kalends|Nones|Ides}}

==Days==
{{main|Kalends}}
Roman dates were [[inclusive counting|counted inclusively]] forward to the next one of three principal days within each month:<ref name=odalay/>

* '''[[Kalends]]''' (''{{lang|la|Kalendae}}'' or ''{{lang|la|Kal.}}''), the first day of each month<ref name=odalay>{{harvp|Beck|1838|p=[https://books.google.com/books?id=uJgQAAAAYAAJ&pg=PA175 175]}}.</ref>
* '''Nones''' (''{{lang|la|Nonae}}'' or ''{{lang|la|Non.}}''), the seventh{{spaces}}day of "full months"<ref name=loser/>{{efn|The original 31-day months of the Roman calendar were March, May, Quintilis or July, and October.|name=four}} and fifth{{spaces}}day of hollow ones,<ref name=odalay/> 8{{spaces}}days before the Ides in every month
* '''Ides''' (''{{lang|la|Idus}}'', variously ''{{lang|la|Eid.}}'' or ''{{lang|la|Id.}}''), the 15th{{spaces}}day of "full months"<ref name=loser/>{{efn||name=four}} and the 13th{{spaces}}day of hollow ones,<ref name=odalay/> one day earlier than the middle of each month.

These are thought to reflect a prehistoric lunar calendar, with the kalends proclaimed after the sighting of the first sliver of the new crescent moon a day or two after the [[new moon]], the nones occurring on the day of the [[first-quarter moon]], and the ides on the day of the [[full moon]]. The kalends of each month were sacred to [[Juno (goddess)|Juno]] and the ides to [[Jupiter (planet)|Jupiter]].{{sfnp|Ovid|loc=Book I, ll. 55–56}}{{sfnp|Kline|2004|loc=[https://web.archive.org/web/20050419220209/http://www.tkline.freeserve.co.uk/OvidFastiBkOne.htm Book I, Introduction]}} The day before each was known as its eve (''{{lang|la|pridie}}''); the day after each (''{{lang|la|postridie}}'') was considered particularly unlucky.

The days of the month were expressed in early Latin using the [[ablative of time]], denoting points in time, in the contracted form "the 6th{{spaces}}December Kalends" (''{{lang|la|VI Kalendis Decembribus}}'').<ref name=loser/> In classical Latin, this use continued for the three principal days of the month<ref name=perdedor>{{harvp|Beck|1838|p=[https://books.google.com/books?id=uJgQAAAAYAAJ&pg=PA177 177]}}.</ref> but other days were idiomatically expressed in the [[accusative case]], which usually [[accusative of time|expressed a duration of time]], and took the form "6th day before the December Kalends" (''{{lang|la|ante diem VI Kalendas Decembres}}''). This anomaly may have followed the treatment of days in [[Ancient Greek language|Greek]],{{sfnp|Smyth|1920|loc=[https://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0007%3Apart%3D4%3Achapter%3D42%3Asection%3D97%3Asubsection%3D89 §§1582–1587]}} reflecting the increasing use of such date phrases as an absolute phrase able to function as the object of another preposition,<ref name=loser>{{harvp|Beck|1838|p=[https://books.google.com/books?id=uJgQAAAAYAAJ&pg=PA176 176]}}.</ref> or simply originated in a mistaken agreement of ''{{lang|la|dies}}'' with the preposition ''{{lang|la|ante}}'' once it moved to the beginning of the expression.<ref name=loser/> In [[late Latin]], this idiom was sometimes abandoned in favor of again using the ablative of time.

The kalends were the day for payment of debts and the account books (''{{lang|la|kalendaria}}'') kept for them gave English its word ''[[calendar]]''. The public Roman calendars were the ''[[fasti]]'', which designated the religious and legal character of each month's days. The Romans marked each day of such calendars with the letters:{{sfnp|Scullard|1981|pp=44–45}}

* '''F''' (''[[Glossary of ancient Roman religion#fasti|fastus]]'', "permissible") on days when it was legal to initiate action in the courts of civil law (''{{lang|la|dies fasti}}'', "allowed days")
* '''C''' (''comitialis'') on ''fasti'' days during which the Roman people could hold [[Legislative assemblies of the Roman Republic|assemblies]] (''{{lang|la|dies comitiales}}'')
* '''N''' (''[[Glossary of ancient Roman religion#nefastus|nefastus]]'') on days when political and judicial activities were prohibited (''{{lang|la|dies nefasti}}'')
* '''NP''' (uncertain){{efn|The NP days are sometimes thought to mark days when political and judicial activities were prohibited only until [[noon]], standing for ''{{lang|la|nefastus priore}}''.}} on public holidays (''[[Glossary of ancient Roman religion#feria|feriae]]'')
* '''QRCF''' (uncertain){{efn|The QRCF days are sometimes supposed, on the basis of the ''Fasti Viae Lanza'' which gives it as ''{{lang|la|Q. Rex C. F.}}'', to stand for "Permissible when the King Has Entered the Comitium" (''{{lang|la|Quando Rex Comitiavit Fas}}'').{{sfnp|Rüpke|2011|pp=26–27}}}} on days when the "king" (''[[rex sacrorum]]'') could convene an assembly
* '''EN''' (''{{lang|la|endotercissus}}'', an [[Old Latin|archaic form]] of ''{{lang|la|intercissus}}'', "halved") on days when most political and religious activities were prohibited in the morning and evening due to [[religion in ancient Rome#Sacrifice|sacrifices]] being prepared or offered but were acceptable for a period in the middle of the day

Each day was also marked by a letter from A to H to indicate its place within the [[nundinal cycle]] of market days.

==Weeks==
[[File:Fasti Praenestini Massimo n2.jpg|thumb|A fragment of the ''[[Fasti Praenestini]]'' for the month of April (''[[Aprilis]]''), showing its nundinal letters on the left side]]
{{main|Nundinae|Planetary hours|Week}}
The [[nundinae]] were the market days which formed a kind of [[weekend]] in [[ancient Rome|Rome]], [[Roman Italy|Italy]], and some other parts of Roman territory. By Roman [[inclusive counting]], they were reckoned as "ninth days" although they actually occurred every eighth day. Because the republican and Julian years were not evenly divisible into eight-day periods, [[fasti|Roman calendars]] included a column giving every day of the year a [[nundinal letter]] from A to H marking its place in the cycle of market days. Each year, the letter used for the markets would shift {{nowrap|2–5 letters}} along the cycle. As a day when the city swelled with rural [[plebeians]], they were overseen by the [[aedile]]s and took on an important role in Roman legislation, which was supposed to be announced for three nundinal weeks (between {{nowrap|17 and 24 days}}) in advance of its coming to a vote. The [[patricians]] and their [[Patronage in ancient Rome|clients]] sometimes exploited this fact as a kind of [[filibuster]], since the [[tribunes of the plebs]] were required to wait another three-week period if their proposals could not receive a vote before dusk on the day they were introduced. Superstitions arose concerning the bad luck that followed a nundinae on the nones of a month or, later, on the [[January Kalends|first day]] of [[January (Roman month)|January]]. Intercalation was supposedly used to avoid such coincidences, even after the Julian reform of the calendar.

The [[7-day week]] began to be observed in [[Roman Italy|Italy]] in the early imperial period,{{sfnp|Brind'Amour|1983|pp=256–275}} as practitioners and converts to eastern religions introduced [[planetary hours|Hellenistic and Babylonian astrology]], the [[Judaism in ancient Rome|Jewish]] [[Saturday]] [[Jewish sabbath|sabbath]], and the [[Christianity in ancient Rome|Christian]] [[Lord's Day]]. The system was originally used for private worship and astrology but had replaced the nundinal week by the time [[Constantine I (emperor)|Constantine]] made [[Sunday]] (''{{lang|la|dies Solis}}'') an official day of rest in AD&nbsp;321. The hebdomadal week was also reckoned as a cycle of letters from A to G; these were adapted for Christian use as the [[dominical letter]]s.

==Months==
The names of Roman months originally functioned as adjectives (e.g., the January kalends occur in the January month) before being treated as substantive nouns in their own right (e.g., the kalends of January occur in January). Some of their etymologies are well-established: January and March honor the gods [[Janus (god)|Janus]]<ref>{{citation |contribution=January, ''n.'' |title=OED }}.</ref> and [[Mars (god)|Mars]];<ref>{{citation |contribution=March, ''n.<sup>2</sup>'' |title=OED }}.</ref> July and August honor [[Julius Caesar]]<ref>{{citation |contribution=July, ''n.'' |title=OED }}.</ref> and his successor, the [[list of Roman emperors|emperor]] [[Augustus]];<ref>{{citation |contribution=August, ''n.'' |title=OED }}.</ref> and the months Quintilis,<ref>{{citation |contribution=†quintile, ''n.<sup>2</sup>'' |title=OED }}.</ref> Sextilis,<ref>{{citation |contribution=sextile, ''adj.'' and ''n.'' |title=OED }}.</ref> September,<ref name=septime>{{citation |contribution=September, ''n.'' |title=OED }}.</ref> October,<ref>{{citation |contribution=October, ''n.'' |title=OED }}.</ref> November,<ref>{{citation |contribution=November, ''n.'' |title=OED }}.</ref> and December<ref>{{citation |contribution=December, ''n.'' |title=OED }}.</ref> are archaic adjectives formed from the [[ordinal numeral|ordinal number]]s from {{nowrap|5 to 10}}, their position in the calendar when it began around the spring equinox in March.<ref name=septime/> Others are uncertain. February may derive from the [[Lupercalia|Februa festival]] or its eponymous ''{{lang|la|februa}}'' ("purifications, expiatory offerings"), whose name may be either [[Sabine language|Sabine]] or preserve an archaic word for [[sulphur]]ic.<ref>{{citation |contribution=February, ''n.'' |title=OED }}.</ref> April may relate to the [[Etruscans|Etruscan]] goddess Apru or the verb ''{{lang|la|aperire}}'' ("to open").{{citation needed|date=March 2017}} May and June may honor [[Maia (goddess)|Maia]]<ref>{{citation |contribution=May, ''n.<sup>2</sup>'' |title=OED }}.</ref> and [[Juno (goddess)|Juno]]<ref>{{citation |contribution=June, ''n.'' |title=OED }}.</ref> or derive from archaic terms for "senior" and "junior". A few [[list of Roman emperors|emperors]] attempted to add themselves to the calendar after Augustus, but without enduring success.

In classical Latin, the days of each month were usually reckoned as:<ref name=perdedor/>

{| class="wikitable" style="white-space: nowrap;" 
|+ Days of the month in the Roman Calendar 
!! colspan=3 style="text-align:right;" | Days in month !! 31d !! 31d !! 30d !! 29d !! 28d
|- style="vertical-align:top;line-height:90%" 
!! colspan=3 style="text-align:right;" | <br>Months before Julian reform !! <small>{{nobold|Mar<br>May<br>Jul<br>Oct}}</small> !! !! !! <small>{{nobold|Jan Apr<br>Jun Aug<br>Sep Nov<br>Dec}}</small> !! <small>{{nobold|Feb}}</small>
|- style="vertical-align:top;line-height:90%" 
!! colspan=3 style="text-align:right;" | <br>Months after Julian reform !! <small>{{nobold|Mar<br>May<br>Jul<br>Oct}}</small> !! <small>{{nobold|Jan<br>Aug<br>Dec}}</small> !! <small>{{nobold|Apr<br>Jun<br>Sep<br>Nov}}</small> !! <small>{{nobold|(Feb)}}</small> !! <small>{{nobold|Feb}}</small>
|- 
! Day name in English !! Day name in Latin !! Abbr !! {{efn|name=four}}{{efn|The months with 31 days before and after the Julian reform – March, May, Quintilis (July), and October – continued using the old system with their Nones on the 7th and Ides on the 15th, making them different from all other months.}} !! {{efn|The months which changed from 29 to 31 days under the Julian reform – January, Sextilis (August), and December – retained their Nones on the 5th and Ides on the 13th, making them different from the other 31-day months but matching all other months.}} !! {{efn| The months which changed from 29 to 30 days under the Julian reform – April, June, September, and November – retained their Nones on the 5th and Ides on the 13th, making them match all other months except those which had had 31 days before the reform.}} !! {{efn| In leap years late in the imperial period, February was reckoned as a 29 day month with all days lasting 24 hours.}} !! {{efn| In leap years early period after the Julian reform, February had 29 days but was reckoned as a 28 day month by treating the sixth day before the March Kalends as lasting for 48 hours.}}
|- align=center style="background-color:lightblue;" 
|align=right|On the Kalends ||align=right|Kalendis ||align=right|Kal. || 1 || 1 || 1 || 1 || 1
|- align=center style="background-color:lavender;"
|align=right|''The day after the Kalends'' ||align=right|''postridie Kalendas''|| ||''2''||''2''||''2''||''2''|| ''2'' 
|- align=center 
|align=right|The 6th day before the Nones ||align=right|ante diem sextum Nonas ||align=right|a.d. VI Non. || style="background-color:lavender" |2 || &nbsp; || &nbsp; || &nbsp; || &nbsp;
|- align=center 
|align=right|The 5th day before the Nones ||align=right|ante diem quintum Nonas ||align=right|a.d. V Non. || 3 || &nbsp; || &nbsp; || &nbsp; || &nbsp;
|- align=center 
|align=right|The 4th day before the Nones ||align=right|ante diem quartum Nonas ||align=right|a.d. IV Non. || 4 || bgcolor=lavender | 2 || bgcolor=lavender | 2 || bgcolor=lavender | 2 || bgcolor=lavender | 2
|- align=center 
|align=right|The 3rd day before the Nones ||align=right|ante diem tertium Nonas ||align=right|a.d. III Non. || 5 || 3 || 3 || 3 || 3
|- align=center 
|align=right|On the day before the Nones ||align=right|Pridie Nonas ||align=right|Prid. Non. || 6 || 4 || 4 || 4 || 4
|- align=center style="background-color:lightblue;" 
|align=right|On the Nones ||align=right|Nonis ||align=right|Non. || 7 || 5 || 5 || 5 || 5
|- align=center style="background-color:lavender;"
|align=right|''The day after the Nones'' ||align=right|''postridie Nonas''|| ||''8''||''6''||''6''||''6''|| ''6'' 
|- align=center 
|align=right|The 8th day before the Ides ||align=right|ante diem octavum Idus ||align=right|a.d. VIII Eid. || bgcolor=lavender | 8 || bgcolor=lavender | 6 || bgcolor=lavender | 6 || bgcolor=lavender | 6 || bgcolor=lavender | 6
|- align=center 
|align=right|The 7th day before the Ides ||align=right|ante diem septimum Idus ||align=right|a.d. VII Eid. || 9 || 7 || 7 || 7 || 7
|- align=center 
|align=right|The 6th day before the Ides ||align=right|ante diem sextum Idus ||align=right|a.d. VI Eid. || 10 || 8 || 8 || 8 || 8
|- align=center 
|align=right|The 5th day before the Ides ||align=right|ante diem quintum Idus ||align=right|a.d. V Eid. || 11 || 9 || 9 || 9 || 9
|- align=center 
|align=right|The 4th day before the Ides ||align=right|ante diem quartum Idus ||align=right|a.d. IV Eid. || 12 || 10 || 10 || 10 || 10
|- align=center 
|align=right|The 3rd day before the Ides ||align=right|ante diem tertium Idus ||align=right|a.d. III Eid. || 13 || 11 || 11 || 11 || 11
|- align=center 
|align=right|On the day before the Ides ||align=right|Pridie Idus ||align=right|Prid. Eid. || 14 || 12 || 12 || 12 || 12
|- align=center style="background-color:lightblue;" 
|align=right|On the Ides ||align=right|Idibus ||align=right|Eid. || 15 || 13 || 13 || 13 || 13
|- align=center style="background-color:lavender;"
|align=right|''The day after the Ides'' ||align=right|''postridie Idus''|| ||''16''||''14''||''14''||''14''|| ''14'' 
|- align=center 
|align=right|The 19th day before the Kalends ||align=right|ante diem undevicesimum Kalendas ||align=right|{{nowrap|a.d. XIX Kal.}} || &nbsp; || bgcolor=lavender | 14 || &nbsp; || &nbsp; || &nbsp;
|- align=center 
|align=right|The 18th day before the Kalends ||align=right|ante diem duodevicesimum Kalendas ||align=right|{{nowrap|a.d. XVIII Kal.}} || &nbsp; || 15 || bgcolor=lavender | 14 || &nbsp; || &nbsp;
|- align=center 
|align=right|The 17th day before the Kalends ||align=right|ante diem septimum decimum Kalendas ||align=right|{{nowrap|a.d. XVII Kal.}} || bgcolor=lavender | 16 || 16 || 15 || bgcolor=lavender | 14 || &nbsp;
|- align=center 
|align=right|The 16th day before the Kalends ||align=right|ante diem sextum decimum Kalendas ||align=right|a.d. XVI Kal. || 17 || 17 || 16 || 15 || bgcolor=lavender | 14
|- align=center 
|align=right|The 15th day before the Kalends ||align=right|ante diem quintum decimum Kalendas ||align=right|a.d. XV Kal. || 18 || 18 || 17 || 16 || 15
|- align=center 
|align=right|The 14th day before the Kalends ||align=right|ante diem quartum decimum Kalendas ||align=right|a.d. XIV Kal. || 19 || 19 || 18 || 17 || 16
|- align=center 
|align=right|The 13th day before the Kalends ||align=right|ante diem tertium decimum Kalendas ||align=right|a.d. XIII Kal. || 20 || 20 || 19 || 18 || 17
|- align=center 
|align=right|The 12th day before the Kalends ||align=right|ante diem duodecimum Kalendas ||align=right|a.d. XII Kal. || 21 || 21 || 20 || 19 || 18
|- align=center 
|align=right|The 11th day before the Kalends ||align=right|ante diem undecimum Kalendas ||align=right|a.d. XI Kal. || 22 || 22 || 21 || 20 || 19
|- align=center 
|align=right|The 10th day before the Kalends ||align=right|ante diem decimum Kalendas ||align=right|a.d. X Kal. || 23 || 23 || 22 || 21 || 20
|- align=center 
|align=right|The 9th day before the Kalends ||align=right|ante diem nonum Kalendas ||align=right|a.d. IX Kal. || 24 || 24 || 23 || 22 || 21
|- align=center 
|align=right|The 8th day before the Kalends ||align=right|ante diem octavum Kalendas ||align=right|a.d. VIII Kal. || 25 || 25 || 24 || 23 || 22
|- align=center 
|align=right|The 7th day before the Kalends ||align=right|ante diem septimum Kalendas ||align=right|a.d. VII Kal. || 26 || 26 || 25 || 24 || 23
|- align=center 
|align=right|The 6th day before the Kalends ||align=right|ante diem sextum Kalendas ||align=right|a.d. VI Kal. || 27 || 27 || 26 || 25 || 24{{efn|After the Julian reform until late in the imperial period, this day was reckoned to last 48 hours during a leap year.}}
|- align=center 
|align=right|The 5th day before the Kalends ||align=right|ante diem quintum Kalendas ||align=right|a.d. V Kal. || 28 || 28 || 27 || 26 || 25
|- align=center 
|align=right|The 4th day before the Kalends ||align=right|ante diem quartum Kalendas ||align=right|a.d. IV Kal. || 29 || 29 || 28 || 27 || 26
|- align=center 
|align=right|The 3rd day before the Kalends ||align=right|ante diem tertium Kalendas ||align=right|a.d. III Kal. || 30 || 30 || 29 || 28 || 27
|- align=center 
|align=right|On the day before the Kalends ||align=right| Pridie Kalendas ||align=right|Prid. Kal. || 31 || 31 || 30 || 29 || 28
|} 
 
Dates after the ides count forward to the kalends of the next month and are expressed as such. For example, March 19 was expressed as "the 14th day before the April Kalends" (''{{lang|la|a.d. XIV Kal. Apr.}}''), without a mention of March itself. The day after a kalends, nones, or ides was also often expressed as the "day after" (''{{lang|la|postridie}}'') owing to their special status as particularly unlucky "black days".

The anomalous status of the new 31-day months under the Julian calendar was an effect of Caesar's desire to avoid affecting the [[Roman festivals|festivals]] tied to the nones and ides of various months. However, because the dates at the ends of the month all counted forward to the next kalends, they were all shifted by one or two days by the change. This created confusion with regard to certain anniversaries. For instance, [[Augustus]]'s birthday on the 23rd{{spaces}}day of September was ''{{lang|la|a.d. VIII Kal. Oct.}}'' in the old calendar but ''{{lang|la|a.d. IX Kal. Oct.}}'' under the new system. The ambiguity caused honorary festivals to be held on either or both dates.

==Intercalation==
{{main|Mercedonius}}
The Republican calendar only had 355{{spaces}}days, which meant that it would quickly unsynchronize from the solar year, causing, for example, agricultural festivals to occur out of season. The Roman solution to this problem was to periodically lengthen the calendar by adding extra days ''within'' February. February was broken into two parts, each with an odd number of days. The first part ended with the Terminalia on the 23rd (''{{lang|la|a.d. VII Kal. Mart.}}''), which was considered the end of the religious year; the five remaining days beginning with the [[Regifugium]] on the 24th (''{{lang|la|a.d. VI Kal. Mart.}}'') formed the second part; and the intercalary month [[Mercedonius]] was inserted between them. In such years, the days between the ides and the Regifugium were counted down to either the Intercalary Kalends or to the Terminalia. The intercalary month counted down to nones and ides on its 5th and 13th day in the manner of the other short months. The remaining days of the month counted down towards the March Kalends, so that the end of Mercedonius and the second part of February were indistinguishable to the Romans, one ending on ''{{lang|la|a.d. VII Kal. Mart.}}'' and the other picking up at ''{{lang|la|a.d. VI Kal. Mart.}}'' and bearing the normal festivals of such dates.

Apparently because of the confusion of these changes or uncertainty as to whether an intercalary month would be ordered, dates after the February ides are attested as sometimes counting down towards the [[Quirinalia]] (February 17), the [[Feralia]] (February 21), or the Terminalia (February 23)<ref>A 94{{nbsp|bc}} inscription.{{which|date=March 2017}}</ref> rather than the intercalary or March kalends.

The third-century writer Censorinus says:
<blockquote>When it was thought necessary to add (every two years) an intercalary month of {{nowrap|22 or 23 days}}, so that the civil year should correspond to the natural (solar) year, this intercalation was in preference made in February, between the Terminalia [23rd] and Regifugium [24th].<ref>Censorinus, ''The Natal Day'', 20.28, tr. William Maude, New York 1900, available at [http://elfinspell.com/ClassicalTexts/Maude/Censorinus/DeDieNatale-Part2.html].</ref></blockquote>

The fifth-century writer [[Macrobius]] says that the Romans intercalated {{nowrap|22 and 23 days}} in alternate years;{{sfn|Macrobius|loc=Book I, Ch. 13, §12}} the intercalation was placed after February 23 and the remaining five days of February followed.{{sfn|Macrobius|loc=Book I, Ch. 13, §15}} To avoid the nones falling on a nundine, where necessary an intercalary day was inserted "in the middle of the Terminalia, where they placed the intercalary month".{{sfn|Macrobius|loc=Book I, Ch. 13, §16, 19}} This appears to have been generally correct. In 170{{spaces}}BC, [[Mercedonius|Intercalaris]] began on the second day after February 23{{sfn|Livy|loc=Book XLIII, Ch. 11, §13}} and, in 167{{spaces}}BC, it began on the day after February 23.{{sfnp|Livy|loc=Book XLV, Ch. 44, §3}}

[[Varro]], writing in the first century{{spaces}}BC, says "the twelfth month was February, and when intercalations take place the five last days of this month are removed."<ref name="Varro">Varro, ''On the Latin language'', 6.13, tr. Roland Kent, London 1938, available at [https://ryanfb.github.io/loebolus-data/L333.pdf].</ref> Since all the days after the Ides of Intercalaris were counted down to the beginning of March, the month had either 27{{spaces}}days (making 377 for the year) or 28 (making 378 for the year).

There is another theory which says that in intercalary years February had {{nowrap|23 or 24 days}} and Intercalaris had 27. No date is offered for the Regifugium in 378-day years.{{sfnp|Michels|1967}} Macrobius describes a further refinement whereby, in one 8-year period within a 24-year cycle, there were only three intercalary years, each of 377{{spaces}}days. This refinement brings the calendar back in line with the seasons and averages the length of the year to 365.25{{spaces}}days over 24{{spaces}}years.

The Pontifex Maximus determined when an intercalary month was to be inserted. On average, this happened in alternate years. The system of aligning the year through intercalary months broke down at least twice: the first time was during and after the [[Second Punic War]]. It led to the reform of the 191&nbsp;BC [[Acilian Law on Intercalation]], the details of which are unclear, but it appears to have successfully regulated intercalation for over a century. The second breakdown was in the middle of the first century&nbsp;BC and may have been related to the increasingly chaotic and adversarial nature of Roman politics at the time. The position of Pontifex Maximus was not a full-time job; it was held by a member of the Roman elite, who would almost invariably be involved in the machinations of Roman politics. Because the term of office of elected [[Magistratus ordinarii / extraordinarii|Roman magistrates]] was defined in terms of a Roman calendar year, a Pontifex Maximus had an incentive to lengthen a year in which he or his allies were in power or shorten a year in which his political opponents held office.

Although there are many stories to interpret the intercalation, a period of {{nowrap|22 or 23 days}} is always {{frac|1|4}}{{spaces}}synodic month short. Obviously, the month beginning shifts forward (from the new moon, to the third quarter, to the full moon, to the first quarter, back the new moon) after intercalation.

==Years==
{{main|List of Roman consuls}}
[[File:Kalender.jpg|thumb|200px|right|A fragment of an imperial [[list of Roman consuls|consular list]]<ref>[[Corpus Inscriptionum Latinarum]] I, CIL VI.</ref>]]
As mentioned above, Rome's legendary 10-month calendar notionally lasted for 304{{spaces}}days but was usually thought to make up the rest of the [[solar year]] during an unorganized winter period. The unattested but almost certain lunar year and the pre-Julian civil year were {{nowrap|354 or 355 days}} long, with the difference from the solar year more or less corrected by an irregular intercalary month. The [[Julian calendar|Julian year]] was 365{{spaces}}days long, with a [[leap day]] doubled in length every fourth year, almost equivalent to the present [[Gregorian calendar|Gregorian system]].

The [[calendar era]] before and under the [[Roman Kingdom|Roman king]]s is uncertain but dating by [[regnal year]]s was common in antiquity. Under the [[Roman Republic]], from 509 BC, years were most commonly described in terms of their reigning [[Roman consul|ordinary consuls]].<ref name=matlock/> ([[Suffect consul|Temporary]] and honorary consuls were sometimes elected or appointed but were not used in dating.)<ref name=matlock/> [[List of Roman consuls|Consular lists]] were displayed on the [[fasti|public calendars]]. After the institution of the [[Roman Empire]], regnal dates based on the emperors' terms in office became more common. Some historians of the later republic and early imperial eras dated from the legendary founding of the city of Rome (''{{lang|la|[[ab urbe condita]]}}'' or {{sc|avc}}).<ref name=matlock/> [[Varro]]'s date for this was 753 BC but other writers used different dates, varying by several decades.{{citation needed|date=April 2017}} Such dating was, however, never widespread. After the consuls waned in importance, most Roman dating was regnal<ref name=matchlock>{{harvp|Mathieson|2003|p=[https://books.google.com/books?id=krcp3GU2MssC&pg=PA15 15]}}.</ref> or followed [[Diocletian]]'s 15-year [[Indiction]] tax cycle.<ref name=matlock/> These cycles were not distinguished, however, so that "year 2 of the indiction" may refer to any of 298, 313, 328, &c.<ref name=matlock/> The [[Greek Orthodox Church|Orthodox]] subjects of the [[Byzantine Empire]] used various Christian eras, including [[Anno Martyrum|those based on Diocletian's persecutions]], [[Incarnation (Christianity)|Christ's incarnation]], and [[Anno Mundi|the supposed age of the world]].

The Romans did not have records of their early calendars but, like modern historians, assumed the year originally began in March on the basis of the names of the months following June. The consul [[Marcus Fulvius Nobilior (consul 189 BC)|M. Fulvius Nobilior]] (r. 189 BC) wrote a commentary on the calendar at his [[Temple of Hercules Musarum]] that claimed January had been named for [[Janus (god)|Janus]] because the god faced both ways,<ref name=Varro />{{where|date=April 2017}} suggesting it had been instituted as a first month.{{citation needed|date=April 2017}} It was, however, usually said to have been instituted along with February, whose nature and festivals suggest it had originally been considered the last month of the year. The consuls' term of office—and thus the order of the years under the republic—seems to have changed several times. Their inaugurations were finally moved to January 1(''{{lang|la|Kal. Ian.}}'') in 153{{nbsp}}BC to allow [[Quintus Fulvius Nobilior|Q. Fulvius Nobilior]] to attack [[Segeda]] in [[Prehistoric Spain|Spain]] during the [[Celtiberian Wars]], before which they had occurred on March 15 (''{{lang|la|[[Ides of March|Eid. Mart]].}}'').{{sfnp|Livy|loc=Book XLVII}} There is reason to believe the inauguration date had been May 1 during the {{nowrap|3rd century BC}} until 222{{nbsp}}BC{{citation needed|date=April 2017}} and [[Livy]] mentions earlier inaugurations on May 15 (''{{lang|la|Eid. Mai.}}''), July 1 (''{{lang|la|Kal. Qui.}}''), August 1 (''{{lang|la|Kal. Sex.}}''), October 1(''{{lang|la|Kal. Oct.}}''), and December 15 (''{{lang|la|Eid. Dec.}}'').{{sfnp|Livy|loc={{pages needed |date=April 2017}}}} Under the Julian calendar, the year began on January 1 but years of the [[Indiction]] cycle began on September 1.

In addition to [[Egyptian calendar|Egypt's separate calendar]], some provinces maintained their records using a local era.<ref name=matlock/> [[Africa (Roman province)|Africa]] dated its records sequentially from 39{{nbsp}}BC;<ref name=matchlock/> [[Roman Spain|Spain]] from AD{{nbsp}}38.{{citation needed|date=April 2017}} This dating system continued as the [[Spanish era]] used in [[medieval Spain]].{{citation needed|date=April 2017}}

==Conversion to Julian or Gregorian dates==
The continuity of names from the Roman to the [[Gregorian calendar]] can lead to the mistaken belief that Roman dates correspond to Julian or Gregorian ones. In fact, the essentially complete [[list of Roman consuls]] allows general certainty of years back to [[expulsion of Tarquin|the establishment]] of the [[Roman Republic]] but the uncertainty as to the end of lunar dating and the irregularity of Roman intercalation means that dates which can be independently verified are invariably weeks to months outside of their "proper" place. Two astronomical events dated by [[Livy]] show the calendar four months out of alignment with the Julian date in 190{{nbsp}}BC and two months out of alignment in 168{{nbsp}}BC. Thus, "the year of the consulship of [[Publius Cornelius Scipio Africanus]] and [[Publius Licinius Crassus Dives (consul 205 BC)|Publius Licinius Crassus]]" (usually given as "205{{nbsp}}BC") actually began on March 15, 205{{nbsp}}BC, and ended on March 14, 204 BC, according to the Roman calendar but may have begun as early as November or December 206{{nbsp}}BC owing to its misalignment. Even following the establishment of the [[Julian calendar]], the leap years were not applied correctly by the Roman priests, meaning dates are a few days out of their "proper" place until a few decades into Augustus's reign.

Given the paucity of records regarding the state of the calendar and its intercalation, historians have reconstructed the correspondence of Roman dates to their Julian and Gregorian equivalents from disparate sources. There are detailed accounts of the decades leading up to the Julian reform, particularly the speeches and letters of [[Cicero]], which permit an established chronology back to about 58{{nbsp}}BC. The [[nundinal cycle]] and a few known synchronisms—e.g., a Roman date in terms of the [[Attic calendar]] and [[Olympiad]]—are used to generate contested chronologies back to the start of the [[First Punic War]] in 264{{nbsp}}BC. Beyond that, dates are roughly known based on clues such as the dates of [[harvest]]s and seasonal [[Roman festivals|religious festivals]].

==See also==
{{Portal|Ancient Rome}}
* [[List of calendars]]
* [[Julian calendar|Julian]], [[Alexandrian calendar|Alexandrian]], [[Byzantine calendar|Byzantine]], & [[Gregorian calendar]]s
* [[Fasti]], [[menologia rustica]], and the [[Calendar of 354]]
* [[List of Roman consuls]] and ''[[ab urbe condita]]'' dating
* [[General Roman Calendar]] of the Catholic Church
* [[Roman festivals]]
* [[Undecimber]]

==Notes==
{{Notelist}}

==References==
===Citations===
{{reflist|20em}}

=== Modern sources ===
{{refbegin|30em}}
* {{cite book |last= |first= |contribution=[[:s:1911 Encyclopædia Britannica/Fasti|Fasti]] |title-link=:s:1911 Encyclopædia Britannica |title=Encyclopaedia Britannica |volume=X |pages=192–193 |date=1911 |editor-last=Chisholm |editor-first=Hugh |display-editors=0 |ref={{harvid|''Enc. Brit.''|1911}} |location=New York |publisher=Encyclopaedia Britannica }}
* {{cite book |last=Beck |first=Charles |url={{google books |id=clMQAAAAYAAJ |plainurl=y}} |title=Latin Syntax, Chiefly from the German of C.G. Zumpt |date=1838 |location=Boston |publisher=Charles C. Little & James Brown |contribution-url=https://books.google.com/books?id=uJgQAAAAYAAJ&pg=PA175 |contribution=Of the Roman Calendar }}
* {{cite book |last=Blackburn |first=Bonnie |author2=Leofranc Holford-Strevens |display-authors=1 |ref={{harvid|Blackburn & al.|1999}} |title=The Oxford Companion to the Year |publisher=Oxford University Press |location=Oxford |date=1999 }}
* {{cite book |last=Brind'Amour |first=P. |title=Le Calendrier Romain: Recherches Chronologiques |location=Ottawa |date=1983 |language=fr }}
* {{cite book |last=Fowler |first=W. Warde |author-link=W. Warde Fowler |title=The Roman Festivals of the Period of the Republic |location=New York |publisher=Macmillan & Co. |date=1899 }}
* {{cite book |last=Grout |first=James |contribution=The Roman Calendar |title=Encyclopaedia Romana |url=https://penelope.uchicago.edu/~grout/encyclopaedia_romana/index.html |publisher=University of Chicago |location=Chicago |contribution-url=https://penelope.uchicago.edu/~grout/encyclopaedia_romana/calendar/romancalendar.html |date=2023 }}
* {{cite book |last=Key |first=Thomas Hewitt |editor=William Smith |editor-link=William Smith (antiquarian) |display-editors=0 |contribution=Calendarium |pages=223–233 |contribution-url=https://penelope.uchicago.edu/Thayer/E/Roman/Texts/secondary/SMIGRA*/Calendarium.html |title=A Dictionary of Greek and Roman Antiquities |date=1875 |publisher=John Murray |location=London }}
* {{cite book |last=Lanfranchi |first=Thibaud |contribution=À Propos de la Carrière de Cn. Flavius |title=Mélanges de l'École Française de Rome: Antiquité |date=October 3, 2013 |volume=125 |issue=1 |doi=10.4000/mefra.1322 |url=http://journals.openedition.org/mefra/1322 |contribution-url=http://mefra.revues.org/1322 }} {{in lang|fr}}
* {{cite book |last=Mathieson |first=Ralph W. |title=People, Personal Expression, and Social Relations in Late Antiquity, ''Vol. II'' |location=Ann Arbor |publisher=University of Michigan Press |date=2003 }}
* {{cite book |last=Michels |first=Agnes Kirsopp Lake |author-link=Agnes Kirsopp Lake Michels |contribution=The 'Calendar of Numa' and the Pre-Julian Calendar |title=Transactions & Proceedings of the APA |volume=80 |location=Philadelphia |publisher=American Philological Association |pages=320–346 |date=1949 }}
* {{cite book |last=Michels |first=Agnes Kirsopp Lake |author-link=Agnes Kirsopp Lake Michels |title=The Calendar of the Roman Republic |location=Princeton |date=1967 |url=https://books.google.com/books?id=FgTWCgAAQBAJ |isbn=978-1-4008-4978-9 }}
* {{cite book |last=Mommsen |first=Theodor |author-link=Theodor Mommsen |title=The History of Rome, ''Vol. I:'' The Period Anterior to the Abolition of the Monarchy |editor-last=Dickson |editor-first=William Purdie |url=https://archive.org/stream/historyrome00dickgoog#page/n6/mode/2up |location=London |publisher=Richard Bentley |date=1864 |ref={{harvid|Mommsen & al.|1864}} }} {{nowrap|[ [http://www.gutenberg.org/cache/epub/10701/pg10701-images.html 1] ]}}
* {{cite book |title=Oxford English Dictionary |location=Oxford |publisher=Oxford University Press }}
* {{cite book |last=Rotondi |first=Giovanni |title=Leges Publicae Populi Romani |location=Milan |publisher=Società Editrice Libraria |date=1912 |language=la }}
* {{cite book |last=Rüpke |first=Jörg |author-link=Jörg Rüpke |title=The Roman Calendar from Numa to Constantine: Time, History, and the Fasti |translator-first=D.M.B. |translator-last=Richardson |publisher=Wiley |date=2011 |isbn=978-0-470-65508-5 |url=https://books.google.com/books?id=pThna2LDwDsC }}
* {{cite book |last=Scullard |first=Howard Hayes |author-link=Howard Hayes Scullard |title=Festivals and Ceremonies of the Roman Republic |publisher=Cornell University Press |date=1981 |location=[[Ithaca, New York|Ithaca]] }}
* {{citation |last=Smyth |first=Herbert Weir |title=A Greek Grammar for Colleges |url=https://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0007%3Apart%3D1%3Achapter%3D1%3Asection%3D1 |publisher=American Book Co. |location=New York |date=1920 }}
* {{cite book |first=Temple |last=Stanyan |title=Grecian History |url=https://archive.org/details/grecianhistoryf00stangoog |location=London |publisher=J. & R. Tonson |date=1707 }}
* {{cite book |title=[[Realencyclopädie der classischen Altertumswissenschaft]] |translator-first=Felix |translator-last=Stokes |editor-last=Von Pauly |editor-first=August Friedrich |editor-link=August Pauly |editor2=Christian Waltz |editor3=Wilhelm Siegmund Teuffel |editor4=Georg Otto August Wissowa |editor4-link=Georg Wissowa |last=Wissowa |first=Georg Otto August |author-link=Georg Wissowa |location=Stuttgart |date=1896 |display-editors=0 |volume=II, Part 2 |pages=2313–2344 |publisher=J.B. Metzlersche Buchhandlung |contribution=Augures |contribution-url=https://sites.google.com/view/pwretranslations/all-articles/2-apollon-barbaroi/augures }}
{{refend}}

=== Ancient sources ===
{{refbegin|30em}}
* {{cite book |author=Marcus Porcius Cato |author-link=Cato the Elder |title=De Agri Cultura |title-link=On Agriculture (Cato) |language=la }}
* {{cite book |author=Marcus Porcius Cato |author-link=Cato the Elder |title=On Agriculture |url=https://penelope.uchicago.edu/Thayer/E/Roman/Texts/Cato/De_Agricultura/A*.html |translator-last=Hooper |translator-first=William Davis |translator2=Harrison Boyd Ash |series=Loeb Classical Library |date=1934 |publisher=Harvard University Press |location=[[Cambridge, England|Cambridge]] |volume=283, Cato vol. III |display-translators=1 }}
* {{cite book |last=Censorinus |author-link=Censorinus |title=[[De Die Natali]] |language=la }}
* {{cite book |last=Censorinus |author-link=Censorinus |translator-last=Maude |translator-first=William |url=https://elfinspell.com/ClassicalTexts/Maude/Censorinus/Contents-Preface-Memoir.html |title=De Die Natali ("The Natal Day") |publisher=Cambridge Encyclopedia Press |location=New York |date=1900 }}
* {{cite book |author=Lucius Junius Moderatus Columella |author-link=Columella |title=[[De Re Rustica (Columella)|De Re Rustica]] |language=la }}
* {{cite book |author=Lucius Junius Moderatus Columella |author-link=Columella |url=https://archive.org/details/bim_eighteenth-century_l-junius-moderatus-colu_columella-lucius-junius_1745 |title=Of Husbandry in Twelve Books and His Book Concerning Trees... |location=London |publisher=[[Andrew Millar]] |date=1745 |translator-last= |translator-first= }}, anonymous translation.
* {{cite book |author=Macrobius Ambrosius Theodosius |title=Saturnalia |url=https://penelope.uchicago.edu/Thayer/L/Roman/Texts/Macrobius/Saturnalia/1*.html |author-link=Macrobius |language=la |ref={{sfnref|Macrobius}} }} 
* {{cite book |author=Macrobius Ambrosius Theodosius |title=Saturnalia, ''Vol. I'' |translator-last=Kaster |translator-first=Robert A. |series=''Loeb Classical Library'', No. 510 |location=[[Cambridge, Massachusetts|Cambridge]] |publisher=Harvard University Press |isbn=9780674996496 |url=https://www.loebclassics.com/view/macrobius-saturnalia/2011/pb_LCL510.3.xml |date=2011 |ref={{harvid|Kaster|2011}} |author-link=Macrobius }} 
* {{Cite wikisource |author=Livy |author-link=Livy |title=From the Founding of the City |translator-last=Roberts |translator-first=Canon |year=1905 |wslink=From the Founding of the City |orig-date=1st century AD |wslanguage=en |ref={{harvid|Livy}} }}
* {{cite book |author=Publius Ovidius Naso | title = Fastorum Libri VI | url=http://www.gutenberg.org/ebooks/8738 | author-link = Ovid |language=la |ref={{sfnref|Ovid}} }} 
* {{cite book |author=Publius Ovidius Naso |title=On the Roman Calendar |url=http://www.poetryintranslation.com/PITBR/Latin/Fastihome.htm |date=2004 |translator-last=Kline |translator-first=Anthony S. |ref={{harvid|Kline|2004}} |publisher=Poetry in Translation |author-link=Ovid }}
* {{cite book |author=Rutilius Taurus Aemilianus Palladius |author-link=Rutilius Taurus Aemilianus Palladius |title=De Re Rustica |title-link=De Re Rustica (Palladius) |language=la }}
* {{cite book |author=Rutilius Taurus Aemilianus Palladius |author-link=Rutilius Taurus Aemilianus Palladius |title=The Fourteen Books of Palladius Rutilius Taurus Aemilianus on Agriculture |url=https://books.google.com/books?id=WoAaAAAAYAAJ |translator-last=Owen |translator-first=Thomas |date=1807 |location=London |publisher=J. White }}
* {{cite book |author=Gaius Plinius Secundus |title=Historia Naturalis |title-link=Pliny's Natural History |author-link=Pliny the Elder |language=la |ref={{sfnref|Pliny}} }}
* {{cite book |author=Gaius Plinius Secundus |title=The Natural History |url=http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.02.0137%3Abook%3D1%3Achapter%3DdedicationT |author-link=Pliny the Elder |translator-last=Bostock |translator-first=John |publisher=Taylor & Francis |date=1855 |location=London |translator2=H.T. Riley |display-translators=1 }}
* {{cite book |author=Plutarch |trans-title=Parallel Lives |title=Βίοι Παράλληλοι |author-link=Plutarch |language=grc }}
* {{cite book |author=Plutarch |translator-last=Perrin |translator-first=Bernadotte |contribution-url=https://penelope.uchicago.edu/Thayer/E/Roman/Texts/Plutarch/Lives/Numa*.html |contribution=The Life of Numa |url=https://penelope.uchicago.edu/Thayer/E/Roman/Texts/Plutarch/Lives/home.html |title=The Parallel Lives, ''Vol. I'' |date=1914 |publisher=Harvard University Press |location=[[Cambridge, Massachusetts|Cambridge]] |series=Loeb Classical Library |ref={{harvid|Perrin|1914}} |author-link=Plutarch }}
* {{cite book |author=Marcus Terentius Varro |author-link=Marcus Terentius Varro |title=Rerum Rusticarum Libri III |language=la |title-link=Rerum Rusticarum }}
* {{cite book |author=Marcus Terentius Varro |author-link=Marcus Terentius Varro |title=On Agriculture |url=https://penelope.uchicago.edu/Thayer/E/Roman/Texts/Varro/de_Re_Rustica/1*.html |translator-last=Hooper |translator-first=William Davis |translator2=Harrison Boyd Ash |series=Loeb Classical Library |date=1934 |publisher=Harvard University Press |location=[[Cambridge, England|Cambridge]] |volume=283 |display-translators=1 }}
* {{cite book |author=Publius Vergilius Maro |author-link=Virgil |title=Georgica |title-link=Georgics |language=la }}
* {{cite book |author=Publius Vergilius Maro |author-link=Virgil |title=The Eclogues and Georgics of Virgil |title-link=:s:Eclogues and Georgics (Mackail 1910)/Georgics 1 |translator-first=John William |translator-last=Mackail |date=1910 |publisher=Longmans, Green, & Co. |location=London }}
{{refend}}

==External links==
*[http://www.instonebrewer.com/TyndaleSites/Egypt/ptolemies/chron/roman/chron_rom_intro_fr.htm Chris Bennett's reconstruction of early Roman dates] in terms of the Julian calendar
*[http://webexhibits.org/calendars/calendar-roman.html Early Roman Calendar – History]
*[http://www.latin.org/datecalculator.php Roman Date Calculator] The North American Institute of Living Latin Studies
*{{cite web | url = http://www.movimentoapostolico.it/new/page.php?p=vangelo&data=01/12/2018&lang=en | title = Theological commentary on the daily Gospel Reading | language = en, fr, es | website = Apostolic Movement (Roman Catholic Church) }}

{{Calendars}}
{{Ancient Rome topics|state=collapsed}}
{{Chronology}}
{{Authority control}}

[[Category:Roman calendar| ]]
[[Category:Calendars]]
[[Category:Culture of ancient Rome|Calendar]]
[[Category:Time in Italy]]