**Peter was crucified upside down**
Peter requested that he be crucified in this position rather than in the position in which Christ died. Did you google it as Mark suggested?
Actually the myth that he was crucified upside down originates in the late 2nd century apocryphal book The Acts of Peter and susequent Clementine literature. Christian writers often erroneously believed some of what was in these obvious works of fiction to be true and repeated the information there as if true when it had no basis in history or reality.
It is a pure myth, probably invented by the disciples of Simon Magus who wanted their founder to be associated with Simon Peter and later venerated as him. And they were successful.
Since the bones of Peter [Simon Bar Jonah] are all intact and accounted for in his ossuary at the Monastery of Dominus Flevit on the Mount of Olives in Jerusalem where they were discovered in 1953, then Peter couldn't have died in Rome.
However it is entirely possible that Simon Magus was crucified upside-down by Nero there in Rome, and his body buried in that pagan cemetery with the other soothsayers on Vatican Hill. Since his mausoleum would have had to have been moved in order for Constantine to build St Peter's Basilica, his bones are more than likely in that tomb under the altar of the basilica. The Vatican should recheck those bones to see if they are the bones of a certain Samaritan sorcerer from Gitto.
And while a person who is crucified actually dies by suffocation, how exactly does someone who is crucified upside down actually die???? and why would the Romans diverge from their normal practice of capital punishment just because someone requests it???
BTW do Catholics have any idea what an UPSIDE DOWN CROSS actually symbolizes??? Do they realize that it is an occult symbol worn by soothsayers and sorcerers?