Historian Dr Michael Scott unlocks the secrets of a mysterious tomb recently discovered in one of Rome's famous catacombs. Found by accident following a roof collapse, the tombs contained over 2,000 skeletons piled on top of each other. This was unlike any other underground tomb ever discovered in Rome. They are located in an area of the catacombs marked as 'X' in the Vatican's underground mapping system - hence the name The X Tombs.