Re-consecrated in 1153 by Count Roger and his wife Adelasia, and entrusted in 1178 to the Augustinian Canons Regular, it became the city’s first parish. Abbots followed one another from 1361 onwards, while sixteenth-century restorations by Fabrizio Moncada and nineteenth-century interventions preserved its integrity. The single-nave, tri-apsed plan recalls Trinitarian symbolism typical of Norman architecture, with pilaster strips and portals of clear transalpine origin opening onto an essential and intimate space.
Inside, the Norman baptismal font, the choir loft of 1877 decorated with episcopal coats of arms, the late Gothic–Baroque frescoes (Saint Monica, Mass of Saint Gregory, Pantocrator), and the sixteenth-century statue of Our Lady of Graces stand alongside a wooden Crucifix of extraordinary workmanship and the Roman funerary urn of Diadumenus, discovered on site and now displayed in the nearby Regional Archaeological Museum.
The friars who lived in the adjoining convent created the recipe for the famous Amaro Averna, which remains secret to this day.