ARNO (anc. Arnus), a river of Italy which rises from the Monte Falterona, about 25 m.
Italy from the Tiber to the Alps, but by the end of the 5th century B.C. it was considerably diminished, and about the year 100 B.C. its boundaries were the Arnus (Arno), the Apennines and the Tiber.
It was separate from Italy proper, the Aesis first and then the Rubicon being the boundary on the east, and the Arnus the boundary on the west, so that, for example, Luca remained outside the boundaries of Italy proper, even in 89 B.C. Romanization had, however, progressed considerably, the foundation of colonies and the construction of roads had gone on during the 2nd century, and the whole district as far as the Padus was given the Roman franchise in 89 B.C., while the Transpadanes received Latin rights, and were fully enfranchised forty years later.