Traditio Legis Sarcophagus: Left end
5th to 8th century
Basilica of Sant'Apollinare in Classe
On the right end of the lid two peacocks approach a cross representing the person of Christ. Peacocks traditionally symbolize eternal life, but in this case they also stand for the faithful who come to Christ. Their beaks touch the cross, perhaps a Eucharistic reference.
Below, on the end of the case, a man with a square beard touches his right hand to the right palm of a younger man while another young man stands with his right hand on his breast. The three all wear togas, signifying high status and authority. The older man has a beard just like the one on St. Peter in the frontal, so most likely he is also Peter.
I would go so far as to suggest that Peter's hand gesture represents the "imposition of hands of the presbyterate" (1 Timothy 4:14). The young man's beardless countenance may be a sign not of youth relative to Peter but of his status as a disciple or successor. The young man on the right would then be someone who has also received this "gift" (ibid.) from Peter and is looking off toward his new mission.
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Photographed at the basilica by Richard Stracke, shared under Attribution-NonCommercial-ShareAlike license.