But there's something else down here that I really want to see. Some of Rome's very first popes were buried in these subterranean tombs. What an extraordinary room this is. This is the crypt of the popes, and nine of the Bishops of Rome are buried here, dating all the way back to the early third century. It's an extraordinary thought that these men were the leaders of Christianity, right at the very beginning, long before the papacy became the office of power, magnificence and wealth that we know today. But some of these Bishops, just like St Peter, were to die for their faith. Sixtus II was celebrating mass right here at the altar when Roman soldiers burst in. When they drew their swords, the entire congregation competed to offer themselves for the honour of martyrdom, at which Sixtus pushed himself forward, bared his neck, and begged them to take his head. The soldiers were happy to take him up on his offer. They beheaded him on the spot.