De Vermis Mysteriis

De Vermis Mysteriis, or Mysteries of the Worm, is a fictional grimoire created by Robert Bloch and incorporated by H. P. Lovecraft into the lore of the Cthulhu Mythos.

The tome first appeared in Bloch's short story "The Shambler from the Stars" (1935), in which a character reads a passage from the book and accidentally summons an extradimensional horror.

Bloch, then a teenager, corresponded with Lovecraft about the story prior to its publication, in part to get permission to kill off a character based on the older writer. While giving his enthusiastic blessing, Lovecraft also suggested that the book featured in the story, named by Bloch as Mysteries of the Worm, be referred to instead by the Latin equivalent De Vermis Mysteriis.

Lovecraft also provided Bloch with a bit of Latin to use as an invocation from the book: "Tibi, magnum Innominandum, signa stellarum nigrarum et bufoniformis Sadoquae sigillum"—which can be translated as "To you, the great Not-to-Be-Named, signs of the black stars, and the seal of the toad-shaped Tsathoggua".

In "The Shambler from the Stars", De Vermis Mysteriis is described as the work of Ludwig Prinn, an "alchemist, necromancer, [and] reputed mage" who "boasted of having attained a miraculous age" before being burned at the stake in Brussels during the height of the witch trials (in the late 15th or early 16th centuries).

Prinn, Bloch writes, maintained that he was captured during the Ninth Crusade in 1271, and attributed his occult knowledge to studying under the "wizards and wonder-workers of Syria" during his captivity. Bloch also associates Prinn with Egypt, writing that "there are legends among the Libyan dervishes concerning the old seer's deeds in Alexandria."

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