St. Peter's Vision of the Cross
Oil on canvas, 94.4 in x 13.7 ft (240 x 420 cm)
Church of Madonna del Orto, Venice, Italy
St. Peter is identified by the papal tiara at his right shoulder and the keys beneath his book (silver for the papacy's temporal authority, gold for its spiritual authority).
The vision is not directly related in any source that I have consulted. The moment pictured appears to be that following Peter's famous encounter with Jesus on the road out of Rome. As the Golden Legend relates, Peter is fleeing the city when he encounters Jesus coming in the other direction. Jesus says he is going to Rome to be crucified again, so Peter resolves to go back and be crucified with him. Then, "our Lord ascended into heaven, Peter beholding it, which wept sore." That the painting relates to Peter's martyrdom is further evidenced by its companion in the church's apse, the Martyrdom of St. Paul.
View this image in full resolution.
Read more about images of St. Peter.
Photographed at the church by Richard Stracke, shared under Attribution-NonCommercial-ShareAlike license.