paul ended up in rome after his arrest in jerusalem. >> you cannot kill me here. i am a roman citizen, and he went to home and the emperor was nero and he was a killer, but in the roman way. the roman cannot be crucified, the romans must be beheaded. >> reporter: the first church here, the constantine basilica was built over peter's tomb, 17 centuries ago, after constantine's conversion. the great roman general, whose victories are evident in the glorious arch near the coliseum had a vision of christ's cross at the battle. his conversion changed the course of history. st. peter was crucified on the vatican hill, not far om the obelisk currently found in st. peter's square. the professor who teaches at the university, recounts the history of that obelisk. >> the story begins in egypt