Baptistère Saint-Jean

The Baptistère Saint-Jean (Baptistery of St. John) is a Roman Catholic church in Poitiers, France. It is reputed to be the oldest existing Christian building in the West and one of the most prominent examples of Merovingian architecture.

The central part of the building was constructed around 360, atop the substructures of Roman buildings that were demolished in 276, in what subsequently became the episcopal quarter of the town of Poitiers, near the residence of Saint Hilary and the future cathedral. Many changes have been made to the original structure. A baptismal tank was added in the 6th century, as at that time baptism was conducted by total immersion.

The building was badly damaged during the Visigoth occupation in the fifth century. A restoration was begun after Clovis I defeated Alaric II in 507 at the Battle of Vouillé, near Poitiers. This restoration included the repair of the upper parts of the walls of the cella, the addition of three apsidioles in the form of a transept and an apse, and the decoration of outside and inside of the building.

By the tenth century the building had become dilapidated, and additions and repairs were made. These included the demolition of two original small sacristies (which were originally designated as preparation chambers for catechumens of both sexes), the lateral apsidioles, the arms of the transept, were rebuilt as apses, and the square narthex was given its present polygonal shape. It was around this time that baptism by immersion had been abandoned as a practice by the Catholic Church, and subsequently, the baptismal pool was filled in and replaced by baptismal fonts. The baptistery then became a parish church.

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