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At 165 pounds, and allegedly made from the skins of 160 donkeys, the Codex Gigas is the world’s largest and most mysterious medieval manuscript.

Filled with satanic images and demonic spells, according to legend, the cursed text sprang from a doomed monk’s pact with the Devil.

Now, Nat Geo follows a team of scientists as they embark on an unprecedented quest to unravel the secrets behind the book’s darkened pages. Using ultra-violet fluorescence imaging, handwriting analysis and a re-creation of the text, forensic document experts attempt to uncover the cryptic truth behind this ancient Devil’s Bible.

The Devil’s Bible is so huge that it requires at least two people to carry it. Once considered the eighth wonder of the world, the Codex Gigas stretches three feet long and weighs a hundred and sixty-five pounds. It is the only book that places the Old and New Testaments alongside violent, holy incantations.

The Codex Gigas contains one full page – right opposite the devil portrait – of a towering Heavenly City. Although no people can be seen in the Heavenly City, it is a symbol of hope and salvation, a contrast to the portrait of the devil on the opposing page.

The Codex Gigas includes mystical medical formulas for anything from treating ailments such as fevers and epilepsy to resolving practical problems such as finding a thief. The book’s transfer to Prague in 2008 took a year of planning.

It was insured for $15.1 million during the transfer. The Devil’s Bible has 600 pages, which is 310 parchment leaves, all made from donkey skins.