The Fall of Simon Magus
12th century (?)
St. Mark's Cathedral, Venice
In the Golden Legend and other sources as old as the second century, Simon Magus promises to fly from a tower to prove his superiority to Saints Peter and Paul. This mosaic illustrates the attempt. Just left of center, Paul kneels in prayer while Peter raises his hand to command Simon's demon helpers to let him fall. (Missing from the composition is the tower from which Simon had leapt.)
Right of center, Peter is crucified upside-down and Paul is beheaded. On the far left, Nero gives the order detailed in the inscription, NERO IMPERATOR UTRISQUE APOSTOLI NECEM DARI ALTERUM CRUCIFIGI ALTERUM GLADIO INTERFICI IUSSIT, "The Emperor Nero orders that both Apostles be killed, the one to be crucified and the other slain by the sword."
I am basing the 12th-century date on Vio's dating of the mosaics to the left of the presbytery (89), but I am not sure that that is where I took the photograph.
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Read more about images of St. Peter and St. Paul.
Photographed at the site by Richard Stracke, shared under Attribution-NonCommercial-ShareAlike license.