The Carcere Mamertino is an ancient Roman prison built in the 4th Century B.C. and used to imprison anyone who it was thought to pose a threat to Rome. It was a dark dank, squalid little underground dungeon that was squashed between the Roman Forum and the Via dei Fori Imperial at the bottom of the steps leading to the Capitoline. The only way into the dungeon was through a hole in the floor. It’s not known how many hundreds of people starved to death and were thrown into the Cloaca Maxima, the city’s main sewer.