The first church outside the walls, dedicated to Saints Nabore and Felice and probably dating back to the 4th century, was destroyed in a fire in 906. It was then decided to rebuild new Cathedral within the walls. The facade is typically Baroque, with red brick wall and marble decorations. The central portal is surmounted by a pediment containing the coat of arms of Benedict XIV supported by two columns. The early Christian bell tower was never demolished and today it can still be admired within the other that was built around it: about 70 meters high, square-based, is a masterpiece in the same style as the church. The interior is a huge bright space, thanks to seven large windows. The rich floor was placed between 1902 and 1905, on the design by Silvio Gordini. The side chapels, five on each side, are topped by crowns that open with chants on the main aisle. In the right nave, the sculptural group in terracotta called "Lament on the Dead Christ" by Alfonso Lombardi, formed between 1522 and 1526. The main altar in polychrome marble is by Alfonso Torreggiani and is surmounted by a valuable Romanesque wooden crucifixion of cedar of the twelfth century. From the main chapel you enter the crypt below.