BAPTISTERY, the hall or chapel connected with a church, in which the sacrament of baptism is administered. The earliest baptistery extant is probably that of the Lateran palace in Rome, which dates largely from the time of Constantine. Octagonal in shape, this baptistery consists of a central area in which was the large octagonal basin or pool called a font, surrounded by eight columns, and an ambulatory (q.v.). The round church of Santa Costanza, in Rome, built, probably, as a tomb for the daughter of Constantine, was also used, in early times, as a baptistery. Fol lowing this tradition, baptisteries, throughout the early Church, were separate buildings, circular or polygonal in plan, up to the 9th or loth century. When the change from immersion to sprink ling as the method of baptism rendered large baptisteries unnec essary, the baptistery became a mere chapel within a church, or even disappeared entirely, the font being placed at any convenient spot. Many baptisteries of the earlier type, especially in Italy, are of great size and richly decorated (Florence, Pisa). In modern usage the baptistery is frequently near the church entrance. The use of immersion, by the modern Baptist Church, has given a new importance to the baptistery in churches of that denomination, where it is often placed immediately behind the chancel, so that the sacrament may take place in the full view of the assembled congregation.
See C. von Hefele, Concilies, passim; Du Cange, Glossary, article "Baptisterium" ; Eusebius, Hist. Eccl. x. 4 ; Joseph Bingham, Antiq uities of the Christian Church, book xi. (1710--2 2) .