You are probably thinking of the Circus of Nero, which was the place where St. Peter was crucified upside-down. Peter was buried in a nearby necropolis, which is now the site of St. Peter's basilica. Drawings I've seen show that the east end of Circus of Nero site intersects the southern portion of St. Peter's Square. Also, the obelisk in the center of St. Peter's Square was previously in the center of the Circus of Nero, similar to the obelisk of the Circus Maximus shown in the video. There are enough similarities between the two places that confusion is understandable.
