The Baptistry (Battistero) was founded in 1152, but it took more than two centuries to be completed. The first stage of construction, up to the top of the first row of arches, was directed by the architect Diotisalvi. At the beginning of the 13th century Guidetto took over and supervised the ornamentation of doors and walls. After 1260, Nicola Pisano worked on the outside wall in the external gallery, but it was Giovanni Pisano who added the pediments above.
The construction followed the proportions of the Cathedral, with which he preserved a perfect axiality: the largeness of the facade exactly corresponds to distance between its main portal and the west door.
Citizens were asked to contribute with a one denaro tax per month, ensuring a good start out of the works. The first colums and pilasters were brought back from the quarries of the Isle of Elba and Sardinia. The dome is skirted by a row of triangular fronted marble aedicules completed with a pair of pinnacles. At the top, the statue in gilded copper of St. John the Baptist (1395).
An imposing building: Eight colums alternating with four pilasters are quite the same height of those of the Cathedral. The access to the upper floor allows to enjoy a spectacular view on the baptismal font of Lombard school, the pulpit of the sculptor Nicola Pisano and the twingled Arabian-style geometries of the pavement. It is the largest Baptistry in the Christian world: 107 meters large, 55 meters high.
An extraordinary echo: The particular inner double-dome allows an exceptional echo, which makes the baptistry a wonderful “musical instrument”. The Opera Primaziale staff on duty gives a “live demonstration of the echo” every half an hour.