Baptistry

Charles Buck Theological Dictionary

The place in which the ceremony of baptism is performed. In the ancient church, it is said, it was generally a building separate, and distinct from the church. It consisted of an ante-room, where the adult persons to be baptized made their confession of faith; and an inner room, where the ceremony of baptism was performed. Thus it continued to the sixth century, when the baptisteries began to be taken into the church.

The Nuttall Encyclopedia

A circular building, sometimes detached from a church, in which the rite of baptism is administered; the most remarkable, that of Pisa.