The baptistery, in Santa Maria Maggiore, was designed by the architect Flaminio Ponzio (1560-1613) in 1605, as part of a programme of additions to the basilica ordered by Pope Paul V (r. 1605-21).
The baptistery was originally the Chapel of the Winter Choir, where the canons celebrated the Divine Office in winter. However, in 1825 Pope Leo XII (r. 1823-29) ordered the canons to move out and commissioned Giuseppe Valadier (1762-1839) to convert the chapel into a baptistery.
Vault
The baptistery comprises two bays: an antechamber and the baptismal chamber. The richly decorated vault of the latter has frescoes by Il Passignano (1559-1638), which depict the Immaculate Conception with Prophets and Doctors of the Church.
The Assumption of the Virgin Mary by Pietro Bernini
The altarpiece is a marble bas-relief of The Assumption of the Virgin by Pietro Bernini (1562-1629), the father of the much more illustrious sculptor Gian Lorenzo Bernini (1598-1680).
The font is an ancient porphyry basin. The gilded bronze statue of St John the Baptist was executed by Giuseppe Spagna to a design by Giuseppe Valadier.
Bust of Pope Benedict XIII by Pietro Bracci
There is a very fine bust of Pope Benedict XIII (r. 1721-24), the work of the Roman sculptor Pietro Bracci (1700-73), on the right side wall.