The Casentino is the valley in which the first tract of the river Arno flows to Subbiano, Italy. It is one of the four valleys in which the Province of Arezzo is divided. Mount Falterona, from which the Arno starts, represents the northern boundary between the Casentino and Romagna. On the east of the valley are the Alpe di Serra and the Alpe di Catenaia, which separate the Casentino from the highest tract of the Val Tiberina.
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