Baptistery, baptismal font and stoup
The baptisteries had been made in a period where the church baptized a big number of catechumen adults and where the baptism by total or partial immersion is the rule (there is a debate here between the historians concerning the height of the pool which was taller than one meter and so would mean that the bishop immerses the head of the catechumen into the water).
Before Constantin and his edit in 313 gave an official status for the Christianity, the baptism by immersion took place in rivers, seas or fountains (witnesses sometimes of a religious syncretism with sacred pagan water springs) or even bathrooms of rich families. We also find few memories of baptisteries before this edit, the oldest is the one of DouraEuropos dated back to the half 3rd century: a room used for baptisms with a cistern probably supplied with earthenware jars under a ciborium and some frescoes. The fresco of the arcosolium is organized in two registers: the Christ as “Good Shepherd on the top, and two men representing the Original Sin at the bottom. From the 4th century until the beginning of the 6th century the baptismal fonts had been set at the porch of the church or inside. They could be also in independent buildings such as the episcopal baptisteries of the cathedrals.
The baptisteries have usually a big size, so high that some councils or synods took place in the baptistery. The excavations in Limoges revealed a baptistery, probably built at the end of the 4th century with an area of 290m² composed of a large hexagonal room and six quadrangular apses on each face of the hexagon. The entrance was on the west.
This big size was explained by several reasons:
-before the 4th century, only the bishop had the authority to baptize the catechumen in his diocese (reason why the baptisteries are usually attached to a cathedral and not a parish church)
-this ritual couldn’t happen more than three times a year (mainly Easter and basically only during this celebration, and Pentecost and Epiphany)
At the end of the 8th century, Pierre Chaunu explained the decline of the baptism by immersion by the “diffusion of the baptism of children in countries where the climate was hard and where we couldn’t immerse the new born in cold water”. In 789, the emperor Charlemagne adopted an adaptation of the catholic baptism, which was then delivered from the birth by a capitular who ordered a simple immersion of the children at their first year, by priests in the parishes and not only by the bishops anymore. This ordonnance was progressively adopted and the baptistery fell into disuse. The archeology shows then shrinkage of pools and their adduction of water disappeared. The baptistery is reemployed for liturgical masses; used as chapel or oratory by setting altars and then it was replaced by simple baptismal fonts in the church.
After the 9th century, a few baptisteries had been built, some remained used, their baptismal pool being covered and surmounted by a cistern. These baptisteries are so replaced by baptismal cisterns.