This Romanesque edifice was built in the 11 and 12C on the site of a former acropolis and was remodelled in the 13C with Gothic additions. Outside you will admire the three Romanesque apses, the Roman campanile, and the statue of the unhappy pope Boniface. The interior contains three aisles laid with Cosmati paving. Notice also the Roman ciborium, paschal candelabrum and Episcopal throne all by Pietro Vassaleto. The crypt is decorated with magnificent 13C frescoes.