Editing Arno (section)

== Source and route ==
[[File:Arno watershed.png|thumb|Map of the Arno River watershed. ]]

The river originates on [[Monte Falterona]]<ref name="LIFE98 NAT/IT/005075">{{cite report |author=Parco Nazionale delle Foreste Casentinesi |date=1999-01-01 |title=Environmental restoration of the area of the river Arno offsprings |url=https://webgate.ec.europa.eu/life/publicWebsite/project/LIFE98-NAT-IT-005075/environmental-restoration-of-the-area-of-the-river-arno-offsprings# |publisher=European Climate, Infrastructure and Environment Executive Agency |access-date=2024-02-16 |quote="...on the southern slopes of Mount Falterona... the springs of the Arno River, described by the great poet Dante Alighieri, and the Etruscan archaeological site Lago degli Idoli are both located here.}}</ref> in the [[Casentino]] area of the [[Apennine Mountains|Apennines]], and initially takes a southward curve. The river turns to the west near [[Arezzo]] passing through [[Florence]], [[Empoli]] and [[Pisa]],<ref name="Encyclopedia Britannica 1998 z588">{{cite web | title=Arno River | website=Encyclopedia Britannica | date=July 20, 1998 | url=https://www.britannica.com/place/Arno-River | access-date=February 16, 2024}}</ref> flowing into the [[Ligurian Sea]]<ref name="Magazine Solly 2018 z520">{{cite web | last1=Magazine | first1=Smithsonian | last2=Solly | first2=Meilan | title=Like a Reverse Atlantis, This Legendary Harbor Ended When Its Sea Route Dried Up | website=Smithsonian Magazine | date=August 24, 2018 | url=https://www.smithsonianmag.com/smart-news/rising-sea-levels-changing-environment-doomed-legendary-pisan-harbor-180970132/ | access-date=February 16, 2024}}</ref><ref name="Encyclopedia Britannica 1965 b099">{{cite web | title=Interesting facts about the Arno River | website=Encyclopedia Britannica | date=March 12, 1965 | url=https://www.britannica.com/summary/Arno-River | access-date=February 16, 2024}}</ref> at [[Marina di Pisa]].<ref name="La Nazione 2023 g129">{{cite web | title=Marina di Pisa, la mareggiata si porta via lo storico retone di Bocca d'Arno | website=La Nazione | date=November 3, 2023 | url=https://www.lanazione.it/pisa/cronaca/retone-boccadarno-mareggiata-sb48sb4d | language=it | access-date=February 16, 2024}}</ref><ref name="PisaToday 2023 c967">{{cite web | title=Mareggiata Marina di Pisa | website=PisaToday | date=November 3, 2023 | url=https://www.pisatoday.it/cronaca/allagamenti-marina-pisa-mareggiata-3-novembre-2023.html | language=it | access-date=February 16, 2024}}</ref>

With a length of {{convert|241|km}}, it is the largest river in the region. It has many tributaries: [[Sieve (river)|Sieve]] at {{convert|60|km|mi}} long, [[Bisenzio (river)|Bisenzio]] at {{convert|49|km}}, [[Ombrone Pistoiese]] at {{convert|47|km}}, and the [[Era (river)|Era]], [[Elsa (river)|Elsa]], [[Pesa (river)|Pesa]], and [[Pescia (river)|Pescia]]. The [[drainage basin]] amounts to more than {{convert|8200|sqkm}} and drains the waters of the following subbasins:

*The [[Casentino]], in the [[province of Arezzo]], formed by the upper course of the river until its confluence with the Maestro della Chiana channel.
*The [[Valdichiana|Val di Chiana]], a plain drained in the 18th century, which until then had been a marshy area tributary of the Tiber.
*The upper [[Valdarno]], a long valley bordered on the east by the [[Pratomagno]] massif and on the west by the hills around [[Siena]].
*The Sieve's basin, which flows into the Arno immediately before Florence.
*The middle Valdarno, with the plain including Florence, [[Sesto Fiorentino]], [[Prato]], and [[Pistoia]].
*The lower Valdarno, with the valley of important tributaries such as the Pesa, Elsa, and Era and in which, after [[Pontedera]], the Arno flows into the [[Ligurian Sea]]. The river has a very variable discharge, ranging from about {{convert|6|m3/s|cuft/s}} to more than {{convert|2000|m3/s|cuft/s}}. The mouth of the river was once near [[Pisa]] but is now several kilometres westwards.
[[File:Ponte Vecchio.jpg|thumb|250px|left|"Ponte Vecchio" (The old bridge) over the Arno in Florence]]
[[File:View From the Ponte Vecchio of the River Arno.jpg|thumb|250px|left|View of the Arno from the [[Ponte Vecchio]]]]
It crosses [[Florence]], where it passes below the [[Ponte Vecchio]] and the [[Ponte Santa Trinita|Santa Trinita bridge]] (built by [[Bartolomeo Ammannati]] but inspired by [[Michelangelo]]). The river [[flood]]ed this city regularly in historical times, most recently in [[1966 flood of the Arno|1966]], with {{convert|4500|m3/s|cuft/s}} after rainfall of {{convert|437.2|mm}} in Badia Agnano and {{convert|190|mm}} in Florence, in only 24 hours.{{Citation needed|date=January 2024}}

Before Pisa, the Arno is crossed by the Imperial Canal at La Botte. This water channel passes under the Arno through a tunnel, and serves to drain the former area of the [[Lago di Bientina]], which was once the largest lake in [[Tuscany]] before its reclamation. 

The flow rate of the Arno is irregular. It is sometimes described as having a torrentlike behaviour, because it can easily go from almost dry to near flood in a few days. At the point where the Arno leaves the Apennines, flow measurements can vary between {{convert|0.56|and|4100 |m3/s|cuft/s}}. New [[dam]]s built upstream of Florence have greatly alleviated the problem in recent years.{{Citation needed|date=February 2023}}

[[File:FirenzeArno1547.jpg|thumb|right|[[High water mark]]s of Arno river floods on August 13, 1547 (left) and November 3, 1844 (metal plate on the right). Photographed in Via delle Casine.]] 

The [[1966 flood of the Arno|flood on November 4, 1966]] collapsed the embankment in Florence, killing at least 40 people and damaging or destroying millions of works of art and rare books.  New conservation techniques were inspired by the disaster, but even decades later hundreds of works still await restoration.<ref>{{cite journal | author = Alison McLean |date=November 2006 | title = This Month in History | journal = Smithsonian | volume = 37 | issue = 8 | pages = 34 }}</ref>