The construction of the bell tower (campanile) was started by Bonanno Pisano with the help of Guglielmo d'Innsburg in 1173. But the work was interrupted when the third floor was finished, as the tower start to lean, as the gound was not stable enough. In that period, the Serchio river was running in the area and the ground was rather wet.
The construction restarted in 1275 by Giovanni di Simone. He added further three storeys, but to avoid further leaning, this part was constructed in such a way to redress the centre of gravity.
Tommaso di Andrea Pisano finished the work in 1350 adding the top floor that houses the bells.
The tower is 55.86 m. high, the diametre of the base is 15 m. and the circumference is 48.62 m., the wall is 4 m. thick (2 m. for the 4th, 5th and 6th storeys). The staircase from the ground level to the bell level counts 293 steps.
Above the entrance to the tower is the statue of Mary and the Infant by Fiorentine artist, Andrea Guardi (15th century).
