Spanning three feet in length and weighing 165 lbs, the Codex Gigas —early 13th century— is the largest medieval manuscript in the world. It is the only book that seems to be simultaneously the Bible, a grimoire, a historical text, and guide to healing. It is also the only Bible that contains an illumination of the Devil.
Even more mysterious is that this book was written by a single hand. The creation of this tome would have taken one man decades to complete. How could this be given that there are no mistakes made in the execution of the book, and that time would have aged the author resulting in inconsistencies in the calligraphy?
According to legend the scribe was a monk who broke his monastic vows and was sentenced to be walled up alive. In order to forbear this harsh penalty he promised to create in one single night a book to glorify the monastery forever, including all human knowledge. Near midnight he became sure that he could not complete this task alone, so he made a special prayer, not addressed to God but to the fallen archangel Lucifer, asking him to help him finish the book in exchange for his soul. The devil completed the manuscript and the monk added the devil's picture out of gratitude for his aid.It is also speculated that the inscription of various exorcism spells is the monk trying to exorcise the devil out by himself. ~Wikipedia
National Geographic link.