The Saint John Baptistery is the oldest Christian building in France, built around 360 A.D, probably by order of Saint Hilaire, the first bishop of Poitiers. It was rebuilt in the VIIth. century. The most important feature of the original building is the octagonal pool, fed by an aqueduct, used for baptisms by immersion. During the visit, one may admire the XIth. century wall paintings as well as the small Merovingian archaeological museum.