The Baptistry of St. John (Battistero di San Giovanni) is a part  of the architectural complex of Siena Duomo. This part of the cathedral complex is on the side of the hill so on the way to the baptistry from Piazza Giacoppo you need go down a beautiful stair.

The Gothic baptistry was designed by architect Camaino di Crescentino between 1316 and 1325. A hexagonal baptismal font in bronze, marble and vitreous enamel, realized in 1417-1431 mostly by Donatello, the most famous sculptor of the time, is in the middle of the baptistry. Some other sculptors of that period also took part in the creation of the font. They are Lorenzo Ghiberti, Goro di Neroccio and Jacopo della Quercia.

The frescoes decorating the walls of the baptistry were created by painter Lorenzo di Pietro (also known as Lorenzo Vecchietta) and his apprentices. Vecchietta also painted two scenes on the wall of the apse: «Flagellation» and «The Road to Calvary».