A baptistery is a religious building used for the Christian ritual of baptism. This was a widespread practice in the first centuries of Christianity, but during the Romanesque period was limited primarily to northern and central Italy. When it was completed, the baptistery in Pisa was the largest in Europe.
Its construction began in 1152 under the direction of the architect Diotisalvi, whose name is mentioned in an epigraph on one of the pilasters in the interior. It has a circular ground plan and the interior is divided into a central space and a circular side aisle by an arcade of alternating pilasters and double columns.
The stonework consists of alternating bands of white and gray marble. The façade is decorated with twenty blind arches pierced by windows, interspersed by the four doors of the baptistery which face the four points of the compass. Above this arcade a cornice supports a loggia of arches resting on slender columns. The upper part was designed by Nicola Pisano and his son Giovanni in the Gothic style sometime after 1277 and was completed at the end of the 14th century.
The ground plan and design of the baptistery resemble that of the Rotunda of Anastasis in the Basilica of the Holy Sepulcher in Jerusalem, which was reconstructed after the Crusades and would have been seen by Pisan crusaders and traders. This link shows the close ties that existed between Pisa and the Holy Land and the important role that Pisa played in the political events of Palestine during the course of the 12th century.
Inside the Baptistery the pilasters and columns support imposing arches on which rests a large colonnaded tribune overlooking the baptismal font. The roof is embellished by a double cupola that appears cone-shaped from the floor of the Baptistery, while on the outside the building is crowned by a noble dome. The granite columns were produced on the islands of Elba and Sardinia and transported to Pisa by sea.
Inside the Baptistery the oldest mantles and capitals are to be found on the first order of columns. They are decorated with figurative motifs, some of which were inherited from antiquity, such as the two-tailed mermaid and scenes of combat between animals and humans, symbolizing the battle between good and evil. These were carved in the atelier of Guidetto, a sculptor from Lombardy who was active at the end of the 12th century. As work continued, a succeeding generation of sculptors trained in the same tradition produced capitals decorated with more stylized masks, human heads and plant motifs; this work was completed around 1230.
In the center of the floor is the monumental baptismal font executed in 1246 by Guido Bigarelli, another sculptor from Lombardy. It is octagonal in form and each of its eight sides is decorated with two rectangles that frame concentric circles embellished with a leaf motif carved in high relief with piercing, and four corners marked by a design in white, red and black marble inlay. Four masks and a central rosette in high relief complete the sculpted decoration. These motifs were inspired by the altar of the Baptistery, whose panels were produced in the workshop of Guglielmo some eighty years earlier, around 1160.
The pilasters flanking the principal portal of the baptistery, which faces east and the Cathedral, have been decorated – on the left with rural scenes representing the twelve months of the year, and on the right with religious scenes including the Ascension of Christ with Mary and the Apostles. The architrave over the door contains scenes from the life of Saint John the Baptist carved by local sculptors under the direction of a master sculptor from Constantinople, and a portrayal of Christ standing between Mary, John the Baptist, the Evangelists and angels.
The Baptistery was completed during the Gothic period with the addition of a fine pulpit decorated with scenes from the life of Christ. These panels, carved in high relief by Nicola Pisano (1260), represent one of the most important works of sculpture produced in 13th-century Europe.