The Battistero di San Giovanni (Baptistery of St John) is believed to be the oldest building in Florence. It stands in the Piazza del Duomo, just to the west of the Duomo. It is believed to date from the 6th or 7th century and was the city's first cathedral, predating Santa Reparata , first recorded as such in 897. It used to be believed that it was originally an ancient Roman temple to Mars, although it is actually almost certainly not a Roman building.

The Baptistery is clad in geometrically patterned marble, reworked in Romanesque style between 1059 and 1128. It is particularly noted for its three sets of magnificent bronze doors.

In 1329, Andrea Pisano was awarded the commission to design the south doors (originally the east doors). The doors, which were completed in 1336 consist of quatrefoil panels, many of which depict scenes from the life of St. John the Baptist.

In 1401, a competition was announced to design the north doors for the baptistery. Seven sculptors competed, including Lorenzo Ghiberti, Filippo Brunelleschi and Jacopo della Quercia, with Ghiberti winning the commission. It took Ghiberti 21 years (1403-1424) to complete these doors. These gilded bronze doors consist of twenty-eight panels, with each depicting a biblical scene from the New Testament.

Ghiberti followed this up with a second set of doors (1425-1452) for the east wall, this time with ten panels depicting scenes from the Old Testament. Michaelangelo referred to these doors as the "gates of paradise", and they are frequently still called this.

The doors now on the Baptistery are now reproductions; the originals are housed nearby in the Museo del Opera del Duomo.

The interior is clad in black and white marble and is crowned by a magnificent mosaic ceiling. The earliest mosaics date from 1225, but they were probably not completed until the 14th century. It depicts the Last Judgment, the rewards of the saved, and the punishments of the damned. This last part is particularly famous. Evil doers are burnt by fire, roasted on spits, crushed with stones, bit by snakes, gnawed and chewed by hideous beasts. Dante Alighieri grew up looking at these mosaics.

The mosaic pavement was begun in 1209. The building contains the tomb of the Antipope John XXIII (d.1419), designed by Donatello and his pupil Michelozzo.

Further Images of the Baptistery