It is located in front of the cathedral façade. The construction of this great building began in the year 1153 under the guide of the architect Diotisalvi, as stated on an epigraph situated inside the monument on a pillar. Hence it was the second monument to rise in the square, given that the works of the church bell-tower (or Leaning Tower) began many years later, i. e. in the year 1174. Also in the case of the Baptistry, as for the other monument of the "Piazza dei Miracoli", from the beginning to the end of the works many years lapsed with interruptions due to different causes. In fact, only at the end of the 14th century the work was terminated.
The Baptistry has a circular base, presents three orders (or stories) and from the third order (or tambour) rises the dome. The height of this imposing monument is 55 mts, with a diameter of 35.50 mts. It has four gates, the principal of which opens towards the façade of the Cathedral. In spite of its gigantic mass, its aspect is refined by a multiple series of ornaments in Gothic style. The first storey is with blind arcades like the Leaning Tower and the Cathedral, but windows have one light. The second order or storey presents an open gallery surmounted by ornamental aedicules with "busts".
There are, furthermore, cusps, on which rest statues of Nicola Pisano and of his school. Such sculptures which, as we have said, are both in the niches and in the cusps of this second storey, are in the most part substituted by copies, while the originals are at the Museum of the "Opera del Duomo". Other cusps magnificently rise, between the aedicules and minor cusps, extending beyond the second order or storey, up to the third order (or tambour), at the same height of the extremely beautiful mullioned windows with two lights which are the main ornament of this storey. Above the third order or storey rises the dome where on there are other windows between the ribs. Regarding the "Entrance Gate" which is in front of the Cathedral façade we will simply list the art represented on this great portal. Here are the sculptures of a unknown author of the 13th century.
On the right hand-post are depicted in relief "The Apostles", "The Descent into Hell" and "David". On the left hand-post are represented "the Months of the Year". The two fillet-architrave presents on the upper part "Jesus between the Virgin and the Baptist, Angels and Evangelists". On the inferior part there is "The History of the Baptist". Above the architrave opens a lunette, that in its centre depicts a copy of the Madonna of Giovanni Pisano. The original of this Madonna of the great master is in the Museum of the "Opera del Duomo". In the sculptured under-arch of the lunette there are shown "The Agnus Dei" and "The 24 Seniors". Also the other portal that faces the walls of the "Churchyard" is magnificently decorated. In the architrave there is a sculpture with "the Annunciation and Saints".