Regolo fled from North Africa to Italy to escape prosecution in the 6th century. He was invited by the Ostrogoth king Totila to attent his court, but he refused. Subsequently he was beheaded. It is said that he picked up his head and walked for a short distance. His remains were transferred to the Duomo in the 8th century.

Also known as the Cathedral of San Martino. It dates from 1060–1070, but it was changed and the façade was added in the 13th century. It was built on a spot of an earlier church.