In 1933 the Byzantine Institute of America began testing the wall where it was believed the great Deesis mosaic might still exist beneath layers of plaster. The first incision in the plaster took place on July 14, 1934. The first season of work took four months and ended in late November of the same year. The panel is 5.95m (19.5 ft) wide and 4.08m (13.5 ft) tall.

Above we can see the ghostly images start to emerge. The painted plaster decoration above the panel was meant to imitate 6th century mosaic work and it comes from a 19th century restoration. The marble vine-leaf cornice is probably from the time of Justinian.

For another four years work continued on the uncovering of the mosaic by Thomas Whittemore and his assistants. The line in the wall shows where brick lines up with stonework

Although the actual removal of plaster took only one year, further seasons of work were required to consolidate and restore the mosaic. Publication of the discovery of the mosaic created a sensation in the art world. Never before had a mosaic of this artistry been seen and the level of technique surpassed anything seen before. The discovery of the mosaic was a sad reminder of how much of Byzantine monumental art has been lost over time.

Although the exact date of the creation of the mosaic is unknown. There are no surviving Byzantine writings that mention it and Byzantine artists usuially did not sign their works. Based on style it is possible to attribute the mosaic to a specific period of Byzantine art from late 12th to mid 13th centuries. It is believed that the mosaic either dates from 1185 - 1204 (in 1204 the city fell to Crusading armies ending all artsistic patronage in the city) - or just after 1261 when the Byzantines regained their capital from the Latin invaders.

The skill with which the mosaic is amazing. The mosaic is laid with astonishing exactness which can especially be seen in the many tiny tessellae making up the faces. A vast number of colors was used in the work and many of the tessellae are laid at angle to take advantage of raking light from a window on the left. This light transfuses the glass tessellae and seems to illuminate them from within. It was immediately apparent to the restorers that a great artist was at work here.

The panel must be the work of a team or mosaic attelier resident in Constantinople for the size of the work would require weeks of work by many skilled craftsmen. Their skill is the accumulated knowlege of generations of artists who created vast expanses of monumental mosaics in golden vaults and domes churches of Constantinople.

It is curious to observe the level of workmanship being applied to such a large panel. The master artist was completely at home in this difficult technique using the skill of a miniaturist on a monumental scale. Considering the limited amount of time the artist has to create the mosaic we can observe in awe his rapid compostion and speed of execution.

After the conquest of the city by the Ottoman Turks in 1453 and the conversion of the church into a mosque many of the mosaics ot the church remained visable, even into the 18th century. It is not known when the Deesis was covered, but it may have been at the direction of an enlightened Sultan wishing to preserve the mosaic from religious zealots.

Not all of the damage to the panel can be attributed to iconoclasts; it seems most of the damage to the figure of the Virgin was most likely caused by the wind and rain from the huge window to her left. For decades wind and rain poured through these windwows which were often open to the outside. elements.