What evidence supports the tradition that St. Peter was martyred in Rome?

The tradition that St. Peter was martyred in Rome is supported by several early Christian sources and historical interpretations, though it is not explicitly detailed in the New Testament.12

The strongest evidence comes from the Letter to the Corinthians (c. 96 CE) by St. Clement of Rome, which describes Peter enduring suffering and bearing witness alongside a "great multitude" of others who faced torture, implying a context of persecution. Additionally, the Gospel of John (21:18–19) refers to Peter's death in the form of a prophecy, and early traditions—such as those found in the writings of St. Ignatius of Antioch—further associate him with the city.1

While the New Testament does not confirm the location, many scholars connect these accounts to the reign of the emperor Nero in 64 CE. Tradition also holds that Peter was crucified upside down, as he reportedly felt unworthy to die in the same manner as Jesus Christ. Archaeological efforts at the Vatican have sought to substantiate these claims, though they remain complex and inconclusive.12