Deesis Mosaic which dates back to the 13th century is thought to occupy the place of an earlier mosaic under it. It is located in the upper south gallery. A production of zenith on mosaic art from the Byzantine times, Deesis Mosaic was depicted in a humanistic style. Due to the open windows left to it, the Virgin part has been damaged for centuries.

In the mosaic; Virgin, St. John the Baptist and the Christ are begging for the salutation of man by showing emotions in a realistic style.

The mosaic is accepted as a pioneer of the Renaissance Art.