View of the focus of the round lower-level chapel that was formerly a prison cell. The chapel is now known as S. Pietro in Carcere. From right to left, note the altar with the upside down cross—according to tradition the Apostle Peter was crucified upside down. The mural above it. To the left of the altar is the remnant of a column which according to tradition the Apostles Peter and Paul were tied to and flogged. In the lower left is what looks like a basin, but actually, there is a small spring there.
According to historical sources, high-status prisoners were detained here from the sixth century B.C. on—including captive kings and rulers. According to Christian tradition, this is where Peter and Paul were kept—at different times, probably while awaiting execution. Of course, Acts 28:30 indicates that Paul spent two "full years in his own rented quarters" (NASB).