Modern Nyon sits on top of Roman Noviodunum — Colonia Iulia Equestris — founded in 45 BCE by Julius Caesar's veterans of the Gallic Wars. The Roman Museum is built into the foundations of the colonia's original basilica, discovered in the 1970s under what is now the Place du Marché. The descent into the basement plunges you straight into stone walls, mosaics, and column bases that have stood here since the 1st century.
Above ground, three tall Corinthian columns reconstructed from original fragments mark the site of the basilica. The museum's collection is small but well-presented and includes mosaics, jewellery, household items, and inscriptions recovered from across the city. Combined ticket with the Lake Museum and the Castle Museum makes sense if you plan to visit more than one. Closed Mondays.