The Sacrifice of Melchizedek
5th century, with medieval and modern restorations
Nave, Basilica of Santa Maria Maggiore, Rome
See Genesis 14:14-20.
This is part of the extensive series of Old Testament scenes portrayed in mosaics along the two walls of the nave. Follow this link for links to the others.
This image in full resolution
More of Abraham
Photographed at the basilica by Richard Stracke, shared under Attribution-NonCommercial-ShareAlike license.