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.
Baptisteries belong to a period of the church when great numbers of adult catechumens were baptized, and when immersion was the rule.
After the 9th century few baptisteries were built, the most noteworthy of later date being those at Pisa, Florence, Padua, Lucca and Parma.
Some of the older baptisteries were very large, so large that we hear of councils and synods being held in them.
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.