Question: I have heard that Peter was crucified upside down. Where does this come from and is it right?
Response: The inverted cross is often attributed to Peter. The tradition that he was crucified on an inverted cross is first found in Eusebius' Ecclesiastical History 2.25.5-8. St. Jerome further records the tradition that this was Peter's request (viz. so as to leave our Lord's death distinctive from his). As to the biblical record, however, all we have is John's testimony of our resurrected Lord's words to Peter to the effect that he would be martyred (Jn.21:18-19). Bibliography can be found in the Oxford Dictionary of the Christian Church or many other good Bible dictionaries or Encyclopediae of the Bible, but the three sources of information given above pretty much sum up the ancient record of what is to be known about this. It is interesting to note that for all the later interest in the manner of the death of the apostles and early believers, the Bible is, in most cases, not particularly forthcoming (cf. the cases of Paul and John, for example, the two most prominent apostles in addition to Peter about whom we have much information in the Bible, but no specifics on their deaths). Perhaps the lesson to be drawn is that we Christians are to make the lives, words and the deeds of these great believers our focus rather than concentrating on the dramatic circumstances of their deaths.
Please see also the following links:
The Deaths of the 12 Disciples / Apostles of Christ.
Martyrdom and Eternal Rewards
Matthias and the Numbering of the Twelve Apostles.
Are there apostles in the Church today?
Apostles and Evangelism
The 12 Apostles of the Lamb
Paul is the 12th Apostle
Yours in Christ,