The cathedral’s subsoil has been studied since 1946. The site has also revealed the remains of two churches, the oldest of which was built around 800 during the time of Charlemagne.

Burial finds and the baptistery uncovered east of the cathedral choir show that one of the earliest Christian communities in the north of the Roman Empire was here.

The excavations have looked at about 4,000 square metres of the cathedral underground, which is still accessible today. You can take a guided tour of the excavation site. This includes a visit to the baptistery and a tour of the cathedral’s show depot to the south. Some other finds are on display in the cathedral treasury.