The construction of the baptistry was started on 15 August 1152, by Pisan architect Diotisalvi. The lower part belongs to this period. It is in Romanesque style, and decorated with half columns and arches similar to those of the Duomo.
The construction was not finished by Diotisalvi, and from 1260, Nicola Pisano started the second phase (the second layer of the building); this part is in Gothic style, with slim columns and trianglular arches. The statues (of Madonna, prophets, evangelists and saints) under the triangluar arches were scrupted by Nicola Pisano and his son Giovanni Pisano. These on site are copies of the original now housed in the Duomo Museum. At the top of each triangles are again statues of saints.
The third layer is characterised by 20 windows and triangular arches, responding to those of the second layer.
The construction of the cupola stared in the 14th century and at the top is the statue of St. John the Baptist. Half of the cupola is covered with red tiles and half with lead plates.
The circumference is 107m., and highth is about 55, without including the topping statue.
The baptisty has for doors toward east, west, south and north, but the most important is the one toward the east, facing to the Duomo. The column on the right side of the gate is scrupted with images taken from the gospels, and on the left columns are symbolic representations of the 12 months. On the architrave, the lower part is decorated with the life of St. John the Baptist, and on the upper part are the statues of Jesus, Madonna, St. John and angels. On the lunetta, there is a copy of the statue, Madonna with the Infant, by Nicola Pisano: the original can be seen in the Duomo museum.
It has undergone several restaurations. The most significant was executed between 1814 and 1856 under the direction of Alessandro Gherardesca, Pietro Bellini and others.
