ALLIA (mod. Fosso Bettinia), a small tributary of the river Tiber, joining it on the left (east) bank, about 11 m. N. of Rome. It gave its name to the terrible defeat which the Romans suffered at the hands of the Gauls on the 18th of July 390 B.C. Livy (v. 37) and Diodorus (v. 114) differ with regard to the site of the battle, the former putting it on the left, the latter on the right bank of the Tiber. Mommsen and others support Diodorus, but the question still remains open.
See T. Ashby in Papers of the British School at Rome, iii. 24.