The cathedral was built around the fifth century on the base of a Roman temple. It has five naves in the city forum. In the eleventh century, after a major restoration and dedication to San Cesareo, the conclave that elected Pope Urban II was celebrated here.
Of artistic interest are the paving of the nave in the style of Cosmati of 1200, and the medieval pulpit held up by five columns. Outside the Romanesque bell tower is elevated off the ground and supported by four pillars.