In the center, below the keystone, is a scene known as the Hetoimasia. It features an empty jeweled emperor's throne, on which is the jeweled case of the True Cross. On the footstool is the Scroll with Seven Seals. St Peter stands to the left, St Paul to the right and above are the symbols of the four Evangelists (Luke's Bull, Matthew's Man, Mark's Lion and John's Eagle). Below is an epigraph reading
Xystus Episcopus Plebi Dei,
("Sixtus the bishop to the People of God")