This detail is of a mosaic in the Baptistery of the Neonians in Ravenna, dating from the late 400s CE. In the dome of the baptistery is a procession of apostles, of which Peter is one. He has already his standard look: a full head of white hair and beard. You can see his name written out in gold: PETRVS. This 1500 year-old depiction of the important saint is one of my favorite. His face, despite the limitations of mosaic, has a real specificity to it and a personality as well. Indeed, each of the apostles in these mosaics seem almost preternaturally individualized, as if the artists had particular friends in mind as models.