The Codex Gigas is the largest surviving medieval manuscript in the world.
At nearly nine inches (22cm) thick and 36 inches (92cm) tall, the book is so large that it is said to have required more than 160 animal skins to complete.
But it's not just its size that has surprised historians.
Inside is a menacing full-page colour image of the Devil, leading many to believe the pages themselves are cursed.
The mysterious manuscript is today housed within the National Library of Sweden in Stockholm and nicknamed 'the Devil's Bible'. The text requires at least two people to lift its 165lbs (74kg) of leather binding and vellum pages.
But how it was created is still unknown.
Legend has it that a monk from the Middle Ages was sentenced to being walled up alive for breaking his monastic vows. To avoid punishment, the monk promised to write, in a single night, a book containing all human knowledge.
As midnight approached, the monk became desperate and turned to Lucifer for help, offering to make a pact to finish the book in exchange for his soul.
Lucifer agreed and signed the work by adding a self-portrait of himself. In the colourful image, he is placed against an empty landscape framed by two large towers.
According to a report by National Geographic several years ago, handwriting analysis by palaeographer Michael Gullick at the National Library of Sweden indicated that one scribe did compose the entire manuscript.
As well as handwriting, a signature within the text – 'hermann inclusis' – points to the fact there was likely to have only been a single author.
The ink is also made from crushed insect nests, and Gullick claims it is highly unlikely one scribe would use different types of ink.
Meanwhile, tests to recreate the calligraphy of the Devil's Bible suggest it would take five years of non-stop writing to create it, according to a report in The Line Up.
'Clearly, the author of this massive tome was possessed by something to create such a masterwork. Whether it was the power of light or darkness, is lost to time,' the report claims.
The Codex Gigas contains five long texts along with the complete Bible.
The book begins with the Old Testament, and it is followed by two works by Flavius Josephus who lived in the first century AD. It ends with the New Testament and the last of the long works is a Chronicle of Bohemia by Cosmas from Prague.
Some researchers believe the legend of the punished monk comes from a misunderstanding in the signature of the book which reads Hermanus inclusus. That single Latin word 'inclusus' was thought to signify a horrific punishment, but the word's true meaning is closer to 'recluse'.
This means the signature could have been made by a solitary monk who chose to shut out the outside world and dedicate his life to the Codex Gigas.
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