The dome is entirely covered with a polychrome mosaic with scenes divided into three sections: the lower frieze shows a hunt; the middle frieze scenes from the Old and New Testaments, separated by columns, and the top frieze shows the four seasons, alternating with four scenes showing a seated personage accompanied by others. The composition converges on a central medallion, of which only a group of small heads remains.
This is the oldest-known dome mosaic with Christian imagery from the Roman world.