The church is divided into nine bays, distinguished by four columns that form a square space in the centre and support the dome. The interior lighting, which creates a rich interplay of light with the mosaic decoration of the floor, the vaults and the sanctuary, is provided by the dome’s eight windows and the ogival-arched windows in the side bays and the apses, which are wider in the arms of the cross than in the four corners. The light penetrates and stands out on the mosaics that, attributable to Byzantine masters, cover most of the walls and vaults.
