The mosaic of the Transfiguration has come down through centuries to bring us the testimony of a religious, symbolic, iconographic, technical and material culture that is far away in time. In fact, the events that have occurred over the years have played an important role in the ageing of the constituent materials of this major work and in the deterioration that threatening its survival.

Earthquakes have put the church and its mosaics under structural stress, which affected the most fragile parts and caused gradual or immediate detachment in several places.

The mortars supporting the mosaic cracked and came away from the church wall; the tesserae began to fall, one by one, in the areas most affected by this phenomenon; rainwater started coming in the windows above the arch and – flowing  over the surfaces –corroded the materials and caused the definitive loss of  tesserae in the area directly beneath.

Right at the fulcrum of the entire decorative scheme, at the center of the apse, infiltrating water with no means of escape weighed down the mosaic’s preparatory layers directly behind the face of Christ and accumulated debris. It caused the most serious detachment at the peak of the concave part of the apse, separating the center of the image from its wall support by at least 10 cm, and causing a bulge that was ready to drop off.

Other areas of the mosaic also risked being lost – for example, the upper scene on the arch depicting the consignment of the Tablets, the right-hand angel and the medallions of the upper apse depicting the apostles Paul and Andrew. The central Cross at the peak of the under-arch was virtually destroyed. Although less serious, other phenomena also contributed to the deterioration of the mosaic’s materials. At the beginning of the conservation program, its appearance was dull and gray, covered by centuries of dust stirred up by the thousands of pilgrims visiting the church, and caught by the greasy elements in candle smoke and the incense used during religious services.