Peter and Paul died in the persecution of the emperor Nero.  Peter was crucified and buried on Vatican hill – the present St. Peter’s basilica was erected over his tomb.  Paul was beheaded and buried outside the walls of the city.  The basilica of St. Paul’s outside the walls covers Paul’s tomb.  The tombs of these two apostles in Rome made Rome the pre-eminent site of Christian pilgrimage from the 4th century to the present, second only to Jerusalem in importance.