The heart of the Piazza del Duomo is the Duomo, the medieval cathedral, entitled to Santa Maria Assunta (St. Mary of the Assumption). This is a five-naved cathedral with a three-naved transept. The church is known also as the Primatial, the archbishop of Pisa being a Primate since 1092.
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 façade, of grey marble and white stone set with discs of coloured marble, was built by a master named Rainaldo, as indicated by an inscription above the middle door: Rainaldus prudens operator.
The massive bronze main doors were made in the workshops of Giambologna, replacing the original doors destroyed in a fire in 1595. The central door was in bronze and made around 1180 by Bonanno Pisano, while the other two were probably in wood. However worshippers never used the façade doors to enter, instead entering by way of the Porta di San Ranieri (St. Ranieri's Door), in front of the Leaning Tower, made in around 1180 by Bonanno Pisano.