Allia is a small river in Lazio, Italy. It is a left tributary of the Tiber with confluence about from Rome. The Allia's source is located in the mountains near the location of Crustumerium and it flows near Monterotondo towards the Tiber. The confluence of Allia and the Tiber is the site of the Battle of the Allia, where Romans were defeated by the Gallic tribe Senones under Brennus in 387 BC. See also References Rivers of Italy Rivers of Lazio Rivers of the Province of Rome