The dungeon, reputedly at the house of Caiaphas (now at the church of St. Peter in Gallicantu), was bellieved to be a place for prisoners. Because the dungeon had such a small opening, individuals had to be fastened with a harness before they could be lowered into the place.
This image of Jesus, affixed with a harness, is at the current church. Click on the image for a better view.
Image online, courtesy Wikimedia Commons.