Walking down the steep Via di San Pietro in Carcere from the Piazza del Campidoglio one enters the northern end of the Forum Romanum, passing on the way the Carcere Mamertino. This is the Mamertine Prison, a dank dungeon where anyone who got on the wrong side of the ancient Roman authorities was thrown. The most famous internee was St Peter who was held here prior to his trail. Being St Peter, he created a miraculous stream of water to baptise his fellow prisoners and dented the wall with his head. The site is now the church of San Pietro in Carcere.