The Saint-Jean baptistery located in Poitiers is a very old Christian monument, the origin of which dates back to the second half of the 4th century, beginning of the 5th century. Although heavily altered over the centuries, it is the building that best illustrates the dependence of Merovingian architecture.

Inside, discover in particular an old octagonal baptismal pool, then used for baptism by immersion until the 8th century. This monument, which has become a parish church, was adorned with a very fine set of Romanesque and Gothic wall paintings in the 11th-12th centuries and in the 13th century.

A remarkable collection of Merovingian sarcophagi is also exhibited here.