The San Vitale Hospitality of Abraham Mosaic: Detail, St. Luke
The ox at the top is the symbol of St. Luke. The Latin phrase in the book is secundum lucam, "according to Luke."
The saint's pallium and the basket of scrolls are conventional attributes of philosophers (Jensen, Face to Face, 44). The water bird in the marsh at the bottom parallels the ducks in the corresponding panel with St. John on the left and the panel for St. Mark on the facing wall.
View this image in full resolution.
View the entire mosaic.
Read more about images of St. Luke.
Photographed at the basilica by Richard Stracke, shared under Attribution-NonCommercial-ShareAlike license.