This compact 10th-century church sits almost at sea level on the edge of the lower old town, its apse hanging over the water. It is one of the oldest surviving churches in Gaeta and one of the most atmospheric: small, dark inside, and built in a hybrid style that shows the Byzantine, Lombard, and early Romanesque influences that converged on southern Italy during the early medieval period.
The church is no longer in regular liturgical use but opens to visitors. The interior retains traces of medieval frescoes and has a characteristic two-storey structure — an upper chapel above a lower crypt — that was common in southern Italian coastal churches of this period. The exterior, seen from the harbour walk, with its striped stonework and arched windows reflected in the water below, is one of the iconic images of Gaeta.