Christ the Way, the Truth, and the Life
Archbishop's Chapel, Ravenna
The pages in the open book read EGO SUM VIA VERITAS ET VITA, "I am the Way, the Truth, and the Life" (John 14:6). The lion and serpent on which Christ is treading are from Psalm 90(91):13, "Thou shalt walk upon the asp and the basilisk: and thou shalt trample under foot the lion and the dragon."
E. B. Smith (153) surveys a number of other early images in which Christ tramples on these symbols of the devil.
This image in full resolution
More of the lion symbol
Also see Christ in Majesty
Photographed at the chapel by Claire Stracke, shared under Attribution-NonCommercial-ShareAlike license.