Exploring Rome's 'sacred sewers'
Built over 2500 years ago, the ancient sewers of Rome used to serve a religious as well as a practical function.
Constructed in the 6th Century BC one of the main functions of the sewers was to drain the Forum, which was periodically flooded by the Tiber. It was the main sanitation system for the city until the 19th Century.
But ancient Romans believed it had another purpose. Removing the waste from the city was seen as a way of purging Rome of evil, as well as preventing disease and flooding.
According to Dr Mark Bradley, associate professor of ancient history at Nottingham University, the bodies of criminals and deposed tyrants were often thrown into the sewers as a ceremonial act.
"These sewers are sacred in part because they flush waste out of the city. They cleanse the city, they make the city pure." he told Simon Sebag Montefiore for BBC Four's Rome: A history of the Eternal City.
He added: "There are shrines marking particular points and junctions in the sewer."
Watch episode one of Rome: A history of the Eternal City on iPlayer
Episode two is broadcast Wednesday 12 December on BBC Four at 2100(GMT)