But it is the less-than-holy legend behind the Codex Gigas that draws most of the attention. According to the Codex legend, the single scribe was a monk who breached his monastic code and was sentenced to be walled up alive with no chance of escape. There was only one way the monk could avoid his excruciating death, he promised to create a beautiful, and fascinating book to glorify the monastery forever; a book that would include all human knowledge. There was one catch—he was given only twenty-four hours to complete the task, and if he succeeded, he'd be free to live.

The monk began to compose a bible written on animal skins, with colored inks and illustrations; completely illuminated (with decorated initials and miniature border artwork) in the manuscript style of that era. Legend has it that near midnight, the monk became sure that he could not complete this task alone, so he sold his soul to the devil for help. The devil completed the manuscript and the monk added the devil's picture out of gratitude. It is because of this unique illustration that it the Codex Gigas is also known as the Devil's Bible.