The Codex Gigas is the largest extant medieval manuscript in the world. It is also known as the Devil’s Bible because of a large illustration of the devil on the inside and the legend surrounding its creation.
According to one version of a legend that is already recorded in the Middle Ages 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 angel 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. In tests to recreate the work, it is estimated that in order to reproduce only the calligraphy, without the illustrations or embellishments, would have taken 5 years of non-stop writing. [from Wikipedia]