Just off the steps leading from the Capitoline hill down to the Roman Forum, the Mamertine Prison was waiting for anyone thought to pose a threat to the security of the ancient Roman state. A dank, dark, tiny underground dungeon, its lower level (built in the fourth century BC) was once only accessible through a hole in the floor. The innumerable prisoners who starved to death here were tossed into the Cloaca Maxima, the city's main sewer. The most famous of the prison's residents, legend has it, were Saints Peter and Paul. The hole in ceiling is where prisoners were lowered down below where a sign reads how prisoners were killed…”Decapitato” (Decapitated), “Strangolati” (Strangled), “Morto Per Fame” (Starved to death).

Peter caused a miraculous well to bubble up downstairs in order to baptize his prison guards, whom he converted by his shining example.

 Paul may have been detained here before he was executed at the Aquas Salvias (at the Abbazia delle Tre Fontane) and Peter before being executed in Nero's circus on Vatican Hill.