The Sarcophagus of Adelphia: Detail, St. Peter, Jesus, and the Rooster
Scenes like this are often taken to refer to Jesus' prediction that Peter will deny him that very night (Matthew 26:31-35, Mark 14:27-31, Luke 22:31-34, John 13:36-38). Some scholars, however, believe the scene is the one in John 21:15-17, where Jesus asks three times, "Peter, do you love me" (Sgarlata, 127). Peter replies three times in the affirmative and Jesus then says, "Feed my sheep." This commission and the parallel between Peter's three denials and his three declarations of love show that he has been forgiven, and the rooster would signify what he is being forgiven for. If true, this alternative interpretation would explain why so many sarcophagi of this era include this scene of sins forgiven.
According to Sgarlata, Peter's finger-to-chin gesture has an unfortunately wide array of significations in classical iconography. Those who prefer to see the scene as representing the prediction can point to instances where the gesture indicates the reception of a caution, while for those who see "feed my sheep" it indicates Peter's sorrow regarding his denials, which are signified by the presence of the rooster.
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Photographed at the Syracuse Archeological Museum, Sicily, by Richard Stracke, shared under Attribution-NonCommercial-ShareAlike license.