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The Arno is a river in the Tuscany region of Italy. It is the most important river of central Italy after the Tiber. == Source and route == The river originates on Mount Falterona in the Casentino area of the Apennines, and initially takes a southward curve. The river turns to the west near Arezzo passing through Florence, Empoli and Pisa, flowing into the Tyrrhenian Sea at Marina di Pisa. With a length of , it is the largest river in the region. It has many tributaries: Sieve at long, Bisenzio at , and the Era, Elsa, Pesa, and Pescia. The drainage basin amounts to more than 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 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 to more than . The mouth of the river was once near Pisa but is now several kilometres westwards. It crosses Florence, where it passes below the Ponte Vecchio and the Santa Trìnita bridge (built by Bartolomeo Ammanati but inspired by Michelangelo). The river flooded this city regularly in historical times, most recently in 1966, with after rainfall of in Badia Agnano and in Florence, in only 24 hours. 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 . New dams built upstream of Florence have greatly alleviated the problem in recent years. The 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 40 years later hundreds of works still await restoration. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Arno」の詳細全文を読む スポンサード リンク
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