ALLIA (mod. Fosso Bettina)  , 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 .