As discussed in an earlier post, Saint Catherine's Monastery in Sinai has been continuously inhabited since the fourth century A.D. Remarkably, a lavish figural mosaic program from the sixth century, occupying the conch of the church's apse and a surrounding triumphal arch, survives to this day.
The Mosaic of the Transfiguration is particularly significant because it gives us insight into pre-iconoclastic Byzantine figural representation, the majority of which was destroyed during the Iconoclast Controversy, lasting roughly from 730 to 842 A.D. For this reason, the recent discovery of the mosaic's unstable condition—understandable given the earthquakes that affect the region and the church's contiguous use—was particularly disturbing.
In order to save this beautiful and historically significant mosaic an intensive conservation program was undertaken starting in 2005 and completed in 2010. The Centro di Conservazione Archeologica (CCA), based in Rome, and its team headed by Professor Roberto Nardi, under the supervision of the Supreme Council of Antiquities of Egypt, directed the project.
When the work commenced, Prof. Nardi discovered that a large percentage of the setting bed of the mosaic was detached from the building structure, with the face of Christ, the central focus of the apse mosaic, separated 10 cm from the wall. Other problems encountered included the following: a high number of tesserae were separated from the setting bed; 20,000 of the original tesserae were lost (surprisingly, only a small fraction of the total!); and the mosaic was obscured by a layer of soot, which developed through the use of candles and incense in liturgical practices for the entirety of the mosaic's history. The CCA's work consisted of the re-consolidation of the mosaic to the wall, application of lime mortar underneath the individual loose tesserae, careful cleaning, and the application of 20,000 new tesserae to fill in the missing gaps. The results of this five-year project, while profound for stabilizing and protecting this significant monument, were also beneficial for the insight it provided into the working practices of sixth-century Byzantine artisans.
In the mid-seventh century, the geographical region of the monastery was absorbed into the world of Islam. Muslim reverence for Mount Sinai ensured the site's protection and continued occupation by a Christian community. Religious tolerance certainly played a factor in the survival of this masterpiece of early Byzantine art. Financial support for the conservation project was provided by the Emir of Qatar, Sheikh Hamad bin Khalifa al Thani, indicating that the value of these mosaics continue to cross cultural and religious boundaries.
 Hieromonk Justin of Sinai, Byzantium and Islam: Age of Transition, 51.