The Arch of Augustus is an important monument constructed in the city of Susa, Piedmont, in the province of Turin. It was originally built at the end of the 1st century BC to record the renewed alliance between Emperor Augustus and Marcus Julius Cottius, a Celto-Ligurian ruler who had been made king and Roman prefect of the Cottian Alps. The arch, together with other remains from the period, such as the Roman amphitheatre and a Roman aqueduct, underscore the importance that the city of Susa had during the Roman period.