This is a piece of the Saint Apollinaris amid sheep, apse mosaic, Sant’ Apollinare in Classe, Ravenna, Italy, ca 533-549.

“On the face of the triumphal arch above,  the image of Christ in the medallion appears in the rainbow-streaked heavens, flanked by four symbolic creatures of the vision of Ezekiel and the Book of Revelation. They stand for the four evangelists: the angel for Matthew, the lion for Mark, the Ox for Luke and the Eagles for John.”

Excerpt from “Gardner’s Art Through the Ages” Eleventh Edition