Christian tradition holds that both Peter and Paul were executed in Rome under Nero in the 60s CE, Peter by crucifixion near a circus on the Vatican Hill and Paul by beheading on the road to Ostia, and it is on the strength of that tradition, not administrative convenience, that Rome rather than Jerusalem or Antioch became the seat of the bishop who claims Peter's spiritual succession. Excavations beneath Saint Peter's Basilica in the twentieth century uncovered a Roman-era necropolis and a shrine that at least matches the traditional site of Peter's burial, though the identification of specific bones as his remains a matter of continuing scholarly caution rather than settled proof.
Beneath and around the city, Christians of the second through fourth centuries dug an extensive network of catacombs, underground galleries used for burial rather than, as popular legend later held, for hiding from persecution, and decorated with some of the earliest surviving Christian art. Once Christianity became the empire's favored and then established religion, Rome's bishops built basilicas over the traditional burial sites of the city's martyrs, and pilgrims have traveled to venerate those sites, and to receive the pope's blessing, in unbroken practice for over a millennium and a half. The city that once fed Christians to its arena now governs, from the same ground, the largest single Christian body in the world, and its catacombs and basilicas remain active pilgrimage sites rather than museum pieces.