The huge façade features grandiose Baroque towers added in the 18C, and the Gothic grace of the three arches above the main doorway and the rose window, all of which date from the 13C. On the interior, beneath the organ (1710), naive frescoes from the late 14C depict the Massacre of the Innocents and the life of St Peter. The huge Baroque altarpiece stands in the Romanesque choir, the vaulted ceiling of which is adorned with polychrome medieval detail. The museum of sacred art is also worth seeing.