The Fall of Simon Magus
12th century (?)
St. Mark's Cathedral, Venice
Just left of center, St. Peter raises his hand to command the demons to let Simon fall while Paul kneels in prayer. 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."
Missing from the composition is the tower from which Simon had leapt.
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.
This image in full resolution
More of St. Peter
More of St. Paul
Photographed at the site by Richard Stracke, shared under Attribution-NonCommercial-ShareAlike license.