The baptistery is the place used for baptism ceremonies. It could be a building annexed to the church, with a polygonal layout, since the early Christian church tended to separate the liturgical area where services were held, reserved for the baptised, from those who had not been baptised. The baptismal font is found inside the baptistery.
In the Monreale Cathedral, after the changes made by Ludovico II de Torres in 1604 and for several decades, the chapel of St John the Baptist served as the Baptistery of the entire Cathedral. Located inside the chapel were the baptismal font (moved under the third arch of the right aisle in 1658) and a sculpture dedicated to St John the Baptist.