It was necessary to make them large, because in the early Church it was customary for the bishop to baptize all the catechumens in his diocese (and so baptisteries are commonly found attached to the cathedral and not to the parish churches), and also because the rite was performed only thrice in the year.
Some of the older baptisteries were very large, so large that we hear of councils and synods being held in them.
The most remarkable of these baptisteries is that in the catacomb of San Pontianus (fig.
After the 9th century few baptisteries were built, the most noteworthy of later date being those at Pisa, Florence, Padua, Lucca and Parma.
Some baptisteries were divided into two parts to separate the sexes; sometimes the church had two baptisteries, one for each sex.
As soon as Christianity made such progress that baptism became the rule, and as soon as immersion gave place to sprinkling, the ancient baptisteries were no longer necessary.
The font itself is interesting for its early form, one common in the chief baptisteries of northern Italy: like an island in the centre of the great octagonal tank is a lobed marble receptacle, in which the officiating priest stood while he immersed the catechumens.
At Ravenna exist two famous baptisteries encrusted with fine mosaics, one of them built in the middle of the 5th century, and the other in the 6th.
Though baptisteries were forbidden to be used as burial-places by the council of Auxerre (578) they were not uncommonly used as such.
We have already spoken of the eucharistic celebrations of which the cubicula were the scene; and still existing baptisteries prove that the other sacrament was also administered there.