The Triumphal Arch at San Vitale

Left side
Right side

6th century
Mosaic
Basilica of San Vitale, Ravenna

Left side in full resolution
Right side in full resolution

Also see close-ups of the medallions for Saints Gervasius, Protasius, Peter, Paul, and Andrew.

Photographed at the basilica by Richard Stracke, shared under Attribution-NonCommercial-ShareAlike license.