It is situated in the upper town and was reconstructed around the 10th century on the remains of the preceding pagan temple. The church’s west-facing structure remains from the Romanic phase of construction while parts of the presbytery with the ambulatory, the western zone of the crypt and the lower part of the bell tower are also original. Before the mid-12th century, the building was completed with the creation of the dome and the completion of the bell tower. During the 18th century, the Romanic vault was demolished due to static problems and it was replaced by a cross-vault in stone, decorated with stucco and paintings by Giovanni Cogrossi. The facade from 1854 was realised in a neo-classic shape. On the inside of the diocesan archive, precious illuminated manuscripts, including the Salterio di Varmondo (10th-11th century) and codes are kept.
