This Romanesque edifice was built in the 11C and 12C on the site of a former acropolis and remodelled in the 13C with Gothic additions. Outside you will admire the three Romanesque apses, the Romanesque campanile, and the statue of unlucky Pope Boniface VIII. The interior contains three naves 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.