The Gothic church of "Santa Maria Maggiore", in the lower town (13th-14th century), has a very fine exterior; the interior, the plan of which is a perfect rectangle, has been spoiled by restoration. Other religious edifices include the Benedictine church of "San Valentino" (mostly remade after World War II, but still including 13th-century frescoes) and the Romanesque monastery of "Sant'Antonio Abate", which housed the remains of Pope Celestine V until 1327. The latter's heart is preserved in the small convent church of the Clarisse (17th century).