The Roman Museum focuses entirely on Aventicum, the Roman capital of the Helvets. This town had 20,000 inhabitants, a number that has never been reached again. Aventicum was fortified with a wall measuring 5.5 km in length and containing 4 gates. 73 towers allowed access to its rampart walk.

At the initiative of Pro Aventico, scientific excavations started in 1885. The vestiges have been presented in the Roman Museum since 1938.

The museum is housed in a fortification tower dating back to the 12th century built on the Roman arenas. It displays mosaics and reliefs, the history and the Romanisation of Aventicum and the private lives of the Helvets. The showpiece of its collection is a golden bust of emperor Marcus Aurelius, discovered in a pipe at Cigognier sanctuary.

The vestiges of the theatre, the amphitheatre, a temple and a sanctuary, the forum thermal baths and the eastern gate of Aventicum are accessible all year round.