The building is a mixture of the Romanesque and Gothic styles, reflecting the length of the period of its construction, from the early 13th to the late 15th century.
The cathedral was built on the site of the former pieve of San Basilio and was under construction from 1204 to 1474, when the upper part of the west front was completed by Leonardo Riccomanni of Pietrasanta.
It has a west front of white marble, featuring a portal with a small Gothic rose window above it, between two side blocks of the 17th century.
The nave is divided into three aisles by two arcades of widely spaced polygonal columns supporting high arches.
[5] The cathedral contains a painting by Francesco Solimena, Renaissance sculptures including altarpieces of the Purification and the Coronation, by Leonardo and Francesco Riccomanni, a terracotta of the school of Luca Della Robbia and two marble busts, of Pope Clement XI and Pope Innocent XI, by Giovanni Baratta.