In ancient times the promontory on which it sits was called ‘Cumero’ from the Greek word ‘Cumer’ and ‘Oro’  which together mean ‘mountain looking at  the sea’. It was later called the hill of San Ciriaco, or Guasco Hill, after major fortifications were built facing the sea under Spanish colonial officer Caesare Guasco in the mid 16th century. The church was built on the remains of an ancient temple destroyed in 558 AD by an earthquake that also destroyed the small town of Numana. 

Above its centralised cross-shaped floor plan is a 12 sided pitched dome with vaulting in the Gothic style.

Lined with metal sheets, experts consider it to be one of Italy's oldest and most perfect domes. Also of note is the portal, a true work of art, while both the inside of the cathedral and the Diocesan museum in the crypt  are well worth a visit.