The Transfiguration

12th century with later modifications
Mosaic
Palatine Chapel, Palermo, Sicily

Elijah is identified by the Greek inscription on the left. Across the top is the Greek word for the Transfiguration, Metamorphosis. Only the figure of John is used to illustrate Matthew 17:6, "the disciples hearing, fell upon their face, and were very much afraid."

The Transfiguration Mosaic at Daphni Monastery
The use of broad "light rays" emanating from Jesus to the five other figures follows the example of an 11th-century mosaic in the Daphni Monastery near Athens. Oddly, the Palatine mosaic does not follow the nearly universal tradition of illustrating Matthew's statement that Jesus' "garments became white as snow."

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More of the Transfiguration

Sources:
Palatine mosaic photographed at the chapel by Richard Stracke, shared under Attribution-NonCommercial-ShareAlike license.
Daphni mosaic: from Wikimedia Commons