Baptistère Saint-Jean

The Baptistère Saint-Jean in Poitiers is the oldest surviving Christian building in France, its walls layering Roman, Merovingian and Romanesque construction across fifteen centuries. The core structure dates to the mid-4th century, repurposed from the bathhouse of a Roman private home and closely associated with Saint Hilary of Poitiers, the city's first bishop. By the 6th century, Merovingian builders transformed it into a proper baptistery; the sunken baptismal pool from that era remains visible in the floor. The stepped gabled exterior recognizable today was shaped in the 11th century, when the building was rededicated to John the Baptist. A small on-site archaeological museum displays early Christian frescoes and funerary objects — the building is open Tuesday through Sunday from 14:00 to 16:00, with an entrance fee.