The doors were moved to the South (from the East side) in 1452. Each door has 14 square panels. Twenty of the panels depict events from the life of John the Baptist while eight at the bottom are personifications of virtues. The foliate borders around the door are from a later date, by Vittorio Ghiberti, son of Lorenzo.

Most famous for its three sets of bronze doors, the Baptistery is the oldest extant building in Florence. Excavations have revealed various floor-levels below the Baptistery's inlaid marble base, and these fragments suggest that there was a building of some size on the site, possibly as early as the Roman period. The date of the present building is controversial, but it is now thought likely that it is a 6th- or 7th-century structure, although it has also been attributed to the 11th century: there was a consecration in 1059. The geometric facing was applied in this period, but the striped angle pilasters were added during the 13th century; the lantern dates from ca. 1150. An inscription on the mosaics of the apse indicates that it was begun ca. 1225 and, according to Giovanni Villani, the mosaics of the main vault were virtually completed by 1325.