The Cluilian trench (Latin: Fossae Cluiliae) was a huge military trench that surrounded ancient Rome about four to five miles outside the city made by the army of Alba Longa during the war between Alba Longa and Rome in the middle of the seventh century BC. It was named after the Alban king, Gaius Cluilius.
Livy speaks of the "Cluilian Trenches" again in a war that took place in the fifth century BC. Here he records that a Volscian army camped at the Cluilian trench and from there ravaged the countryside.
Plutarch in his Lives of the noble Grecians and Romans also speaks of these as the "Cluilian ditches" and describes the same army of the Volsci encamped at a place five miles outside the city called the Cluilian ditches.