The Codex Gigas includes the entire Latin Bible. It also contains many other popular writings of its time, also written in Latin, including additional religious writings, reference books, and medical texts. It seems to be an early encyclopedia—an attempt to collect all the world’s knowledge between two covers. It initially held about 320 pages, but some were removed. No one knows who removed the pages, or why. However, according to popular myth, the missing pages actually contained an apocalyptic text known as “The Devil’s Prayer”, which was intentionally removed to avoid the destruction of the world.

The manuscript is sectioned off into different parts. About half of the codex focuses on the Latin Bible. It then continues to the history of the Jews, recounting the Genesis creation, including illustrations of Heaven and Earth along the margins. The Codex Gigas also incorporates the New Testament and pages of common prayers and conjurations.

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Despite covering plenty of texts, the Codex Gigas also has many elaborate illuminations, or elaborate illustrations that enhance and accentuate the text. The Codex Gigas contains illuminations and calligraphy in red, blue, yellow, green, and gold. The first page has two Hebrew alphabets with a few additional touches throughout: Church Slavic and Glagolitic alphabets, and Greek alphabets.

Clearly, it's a remarkable work. But perhaps the most noteworthy detail about the Codex Gigas, and certainly the most haunting, is the full-page incarnation of Lucifer, the Fallen Angel, on page 290. It is this infamous illustration that gives the book its nickname and its sinister reputation. The Devil is shown crouching, as if ready to jump out of the page. He has a green face, small red eyes, red horns, red claws, and two red tongues.