It has been supposed that the sanctuary might have been even more ancient, perhaps a Christian adaptation of an already existing temple: the church is in fact located in front of the sacred campus dedicated to Rediculus, the Roman "God of the Return".

This campus hosted a sanctuary for the cult of the deity that received devotion by travellers before their departure, especially those going to face long and dangerous journeys to far-off places like Egypt, Greece or the East.

The two footprints on a marble slab at the center of the church — nowadays a copy of the original, which is kept in the nearby Basilica of San Sebastiano fuori le mura — are popularly believed to be a miraculous sign left by Jesus.

An inscription above the front door on the church's façade used to say: "Stop your walking, traveller, and enter this sacred temple in which you will find the footprint of our Lord Jesus Christ when He met with St. Peter who escaped from the prison.

[citation needed] There is also a modern column with a bust of Henryk Sienkiewicz, the Polish author of the famous historical fiction novel Quo Vadis: A Narrative of the Time of Nero (1886).