If you've never seen actual Roman mosaics before, be prepared to exclaim 'wow!' at the extraordinary Römisch-Germanisches Museum, adjacent to the Dom. Sculptures and ruins displayed outside are merely the overture to a full symphony of Roman artefacts found along the Rhine. Highlights include the giant Poblicius tomb (AD 30–40), the magnificent 3rd-century Dionysus mosaic around which the museum was built, and astonishingly well preserved glass items. Insight into daily Roman life is gained from such items as toys, tweezers, lamps and jewellery, the designs of which have changed surprisingly little since.

Plenty of remnants of the Roman city survive around the museum, including a street leading to the harbour and two wells. Other vestiges from the ancient settlement include a Roman arch from the former town wall outside the Dom and the Römerturm, a tower standing among buildings at the corner of St-Apern-Strasse and Zeughausstrasse.