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