Construction was begun in 1064 by the architect Busketo, and set the model for the distinctive Pisan Romanesque style of architecture. The mosaics of the interior, as well as the pointed arches, show a strong Byzantine influence. [...]
The interior is faced with black and white marble and has a gilded ceiling and a frescoed dome. It was largely redecorated after a fire in 1595, which destroyed most of the medieval art works. Fortunately, the impressive mosaic, in the apse, of Christ in Majesty, flanked by the Blessed Virgin and St. John the Evangelist, survived the fire. It evokes the mosaics in the church of Monreale, Sicily. Although it is said that the mosaic was done by Cimabue, only the head of St. John was done by the artist in 1302 and was his last work, since he died in Pisa in the same year. The cupola, at the intersection of the nave and the transept, was decorated by Riminaldi showing the ascension of the Blessed Virgin.
Galileo is believed to have formulated his theory about the movement of a pendulum by watching the swinging of the incense lamp (not the present one) hanging from the ceiling of the nave. That lamp, smaller and simpler than the present one, it is now kept in the Camposanto, in the Aulla chapel.
The impressive granite Corinthian columns between the nave and the aisle came originally from the mosque of Palermo, captured by the Pisans in 1063. The coffer ceiling of the nave was replaced after the fire of 1595. The present gold-decorated ceiling carries the coat of arms of the Medici.
The elaborately carved pulpit (1302-1310), which also survived the fire, was made by Giovanni Pisano and is one the masterworks of medieval sculpture. It was packed away during the redecoration and was not rediscovered and re-erected until 1926. The pulpit is supported by plain columns (two of which mounted on lions sculptures) on one side and by caryatids and a telamon on the other: the latter represent St. Michael, the Evangelists, the four cardinal virtues flanking the Church, and a bold, naturalistic depiction of a naked Hercules. A central plinth with the liberal arts supports the four theological virtues. The present day reconstruction of the pulpit is not the correct one. Now it lies not in the same original position, that was nearer the main altar, and the disposition of the columns and the panels are not the original ones. Also the original stairs (maybe in marble) were lost.