Editing Roman calendar (section)

{{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]].