Aventicum, the site of the former capital of the ancient Helvetii the Romans founded and built in the 1st century AD, in the town of Avenches (Aventicum in Roman times) in the canton (state) of Vaud, Switzerland. It flourished into the 3rd century and at the time, Aventicum, a walled city, was much bigger than today's Avenches. The Roman amphitheater had a capacity for 10-12,000 spectators. The square tower above the entrance is a medieval addition and now houses the museum displaying all the finds made on the grounds of the ancient city.