The Brotherhood of Demnos, also known as the Cult of Demnos, was a cult in San Martino in 1492. 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 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)

After the cult's defeat, Duke Giuliano organised the survivors into a beneficent group known as the Orbus Postramo. Over time, they took Giuliano's diary the Book of Tomorrows as their holy book, which narrated a coming End of Days when the Helix would return, indicated by the appearance and/or death of a herald: Sarah Jane Smith. One faction, the Crimson Chapter, wanted to kill the herald and bring about the end of Humanity. The other faction, the White Chapter, wanted to help the herald bring an age of enlightenment. (AUDIO: Fatal Consequences, Dreamland)

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