The Baptistry of St. John (Italian: Battistero di San Giovanni) is a religious building in Pisa, Italy. It started construction in 1152, in replacement of an older baptistry, and completed in 1363. It's the second building, in the chronological order, in the Piazza dei Miracoli, near the Cathedral and the famous Leaning Tower.
The architect was Diotisalvi, whose signature can be read on two pillars inside the building, with the date 1153:
MCLIII, MENSE AUGUSTI FUNDATA FUIT HAEC ECCLESIA DEUSTESALVET MAGISTER HUIUS OPERIS The structure is 54.86 m high, with a circumference of 107.24 m, and is the largest baptistry in Italy. The Baptistry has an example of the transition from the Romanesque style to the Gothic style: the lower registers are in the Romanesque style, with rounded arches, while the upper registers are in the Gothic style, with pointed arches. The Baptistry is constructed of marble, plentiful and often used in Italian architecture.
The portal, facing the facade of the cathedral, is flanked by two classical columns, while the inner jambs are executed in Byzantine style. The lintel is divided in two tiers. The lower one depicts several episodes in the life of St. John the Baptist, while the upper one shows Christ between the Madonna and St John the Baptist, flanked by angels and the evangelists.
The interior is overwhelming lacks decoration. The octagonal font at the centre dates from 1246 and was made by Guido Bigarelli da Como. The bronze sculpture of St. John the Baptist at the centre of the font, is a work by Italo Griselli.
The pulpit was sculpted between 1255-1260 by Nicola Pisano, father of Giovanni, the artist who produced the pulpit in the Duomo. The scenes on the pulpit, and especially the classical form of the naked Hercules, show at best Nicola Pisano's qualities as the most important precursor of Italian renaissance sculpture by reinstating antique representations. Therefore, surveys of the Italian Renaissance usually begin with the year 1260, the year that Nicola Pisano dated this pulpit.
Constructed on the same unstable sand as the Tower, the Baptistry (as well as the Cathedral) leans 0.6 degrees toward the cathedral.
Originally the shape of the Baptistery, according to the project by Diotisalvi, was different. It was perhaps similar to the church of Holy Sepulchre in Pisa, with his pyramidal roof. After the death of the architect, Nicola Pisano continued the work changing the style to the more modern Gothic one. Also an external roof was added giving the shape of a cupola. As a side effect of the two roofs, the pyramidal inner one and the round external one, the interior is acoustically perfect, working that space as a resonating chamber.