ARNUS, now Arno, a very rapid river of Tuscany, which it divides, and in its course washes Florence and Pisa; rising in the Apennine, to the east of Florence, near a village called S. Maria della Gratie, on the borders of Romagna, 15 miles to the west of the sources of the Tiber; and then turning southward towards Arretium, it is there increased by the lakes of the Clanis; after which it runs westward, dividing Florence into two parts, and at length washing Pisa, falls eight miles below it into the Tuscan sea.