This church, built by the great Admiral of Ruggero II, Giorgio dAntiochia, originally had only one centred Byzantine module, (a four-sided portico with lancet arches resting on high pulvinos and underlying columns), with three apses and a cupola, resting on the octagonal tambour visible from the outside, decorated with cornices and rincassi that are reminiscent of old Byzantine types like Calat Seman. Since the middle ages, it has undergone many transformations and additions, mostly during the Baroque period. The western entrance is composed of a bell tower with a porch of particular architectonic beauty. It has superimposed, and tapered upwards, prismatic volumes of a clear Norman origin, like the little corner towers with columns, common in the bell towers of the Calvados churches. The roof structure is uncertain: pointed or with a cupola. The interior is covered with precious mosaics. In 1184 at Christmas an Andalusian-Arab travelling chronicler, Ibn Jubair, described this church as: " the most beautiful monument in the world".. The pictures show: the bell tower; the octagonal tambour with the superimposed cupola, the same cupola seen from the inside; one of the internal mosaics, with the only existing image of King Ruggero II in the act of being crowned by Christ, and a precious wooden carved tile (of Islamic handicraft) belonging to one of the internal doors of the church.
Guido Di Stefano, "Monumenti della Sicilia Normanna", Palermo, 1979
Melo Minnella Palermo