The Brotherhood of Demnos, also known as the Cult of Demnos, was a cult in San Martino in the 15th century. It worshipped the Roman god of moonlight and practised human sacrifice. Its leader, Hieronymous, was the court astrologer, and secretly aided Count Federico in his plans to to seize power, while planning for the Brotherhood to become the true power in San Martino. The Mandragora Helix also planned to use the Brotherhood to keep Europe in the Dark Ages, but all these plots were defeated by the Fourth Doctor. (TV: The Masque of Mandragora)