The theme is Christ presiding over His Apostles in an arcaded courtyard, wearing Roman robes. Two figures of the apostles have been destroyed; the two nearest Christ are St Peter on the left, and St Paul (replacing Judas) on the right. There is some disagreement about the two female figures behind the apostles - they may be Sts Pudentiana and Praxedes, but they may also represent 'Church' and 'Synagogue', the Gentile and Jewish elements of early Christianity. In that case the Jewish Christian church crowns St. Peter and the Gentile-Christian church crowns St. Paul.

The buildings in the background may be the churches built by emperor Constantine in Jerusalem rather than a depiction of Heavenly Jerusalem. Above Christ is the gemmed cross, as Constantine is said to have marked Calvary with such a monument. Next to the cross are symbols of the Evangelists; this is the oldest preserved example of these symbols.