The case in 60 seconds
Codex Gigas is an extraordinary manuscript. What makes it mysterious, however, is not “supernatural authorship”, but its exceptional size, apparent production by a single hand, and the legend that later grew around it.
The work is a vast Latin manuscript made in early-thirteenth-century Bohemia. It contains biblical texts, Josephus, Isidore's Etymologiae, medical texts, Cosmas's chronicle of Bohemia, a calendar, prayers and some magical/protective formulas.
The story that “a monk finished it in one night with the Devil's help” is not a historical record, but a legend shaped at a later date. Much of the handwriting does appear to belong to one scribe—but that does not mean the book was written in a single night.
The claim
“A monk was sentenced to be walled up alive for breaking monastic rules. To save himself, he promised to write a book containing all human knowledge in one night. At midnight he realised he would not finish, made a pact with the Devil, and the Devil completed the book. In gratitude, the monk painted his portrait.”
This story lies at the heart of Codex Gigas's popular identity. Yet no contemporary document confirms the event, and the details of the legend vary between sources.
What we know
The evidence
1 — The texts and contents are medieval, not supernatural
Codex Gigas contains texts known and circulating in the thirteenth-century Latin Christian world: the Vulgate Bible, the works of Josephus, Isidore's Etymologiae, medical compilations and Cosmas's chronicle of Bohemia. Its contents therefore do not appear to come from an “unknown source”.
Very strong2 — The Devil portrait is consistent with the book's context
Although the full-page Devil portrait is unsettling and unusual, the Heavenly City faces it. This composition can be read as a contrast between salvation and damnation. Depicting the Devil does not, by itself, show that the book glorifies him.
Strong in context3 — “Written in one night” is inconsistent with physical production
Producing so large a parchment codex requires many stages: processing skins, preparing and ruling pages, writing hundreds of thousands of words, rubrication and decoration. Production by a single hand does not mean production in a single sitting.
Modern popular estimates sometimes suggest a production period of around 20–30 years. This is not a precise calculation, but no such figure is needed to show that the “one night” legend cannot be historical.
Clearly inconsistent with the legend4 — The legend is not a contemporary production record
There are different versions of the Devil's assistance. Sources treat the story as a later tradition rather than a direct thirteenth-century production record. Changing details—the Devil bringing the book, supplying materials or assisting with the writing—show how the legend developed over time.
A clear historical distinction5 — The book's journey can be documented
Codex Gigas passed from monastic communities in Bohemia to Habsburg Emperor Rudolf II's collection in Prague. In 1648, at the end of the Thirty Years' War, Swedish forces took it from Prague as war booty. It subsequently reached the royal library in Stockholm and is now held by the National Library of Sweden.
Documented historyTimeline
Codex Gigas is produced in Bohemia.
The work moves between religious institutions in Bohemia; its use in connection with local historical records continues.
It enters Rudolf II's collection in Prague.
It is taken as war booty during the Swedish forces' sack of Prague.
It enters the Royal Library's collection in Stockholm.
It survives the fire at Stockholm's Royal Palace.
It is preserved at the National Library of Sweden and can be studied digitally.
Theories
Theory A — A single monk/scribe worked over many years
Strength: The handwriting's high consistency supports a single main scribe. A large monastic project lasting many years is historically unremarkable.
Weakness: The scribe's identity is uncertain, and the working period cannot be calculated in exact years.
Theory B — An attempt to create a “world of knowledge in one volume”
Strength: The combination of Bible, history, medicine, encyclopaedic material, local chronicle and calendar supports this idea.
Weakness: There is no explicit statement in the author's own preface saying “my aim is to gather all human knowledge into one book”.
Theory C — The Devil and the Heavenly City form a moral contrast
Strength: The placement of two full-page illustrations opposite each other suggests a deliberate theological contrast.
Weakness: No contemporary commentary explains this meaning; it remains an iconographic interpretation.
Theory D — The legend arose later because of the book's size and Devil illustration
Strength: Exceptional size, a single hand and an unsettling full-page Devil image are ideal ingredients for a dramatic origin story.
Weakness: Tracing exactly when the legend first emerged and all the stages of its development is difficult.
Viral claims: are they true?
| Claim | Assessment | Why? |
|---|---|---|
| “The book was written in one night.” | Legend | The scale of production and preparation of materials do not support this historically; no contemporary record exists. |
| “The Devil wrote the book.” | No evidence | This belongs to a later folkloric account. |
| “The entire book was made by one person.” | Largely true | Palaeographic consistency strongly supports a single main scribe. |
| “It contains a book of black magic.” | Exaggerated | It contains prayers, exorcism/adjuratory texts and some talismanic/protective formulas, but the whole work is not an occult grimoire. |
| “The Devil is pictured halfway through the book, and it is the only large illustration.” | An incomplete account | The Devil image is striking, but it faces a Heavenly City illustration of the same scale. |
| “Some pages were deliberately destroyed because they contained terrible secrets.” | No evidence | Leaves are missing, but when and why they were removed is uncertain. Sensational claims about their contents are speculation. |
| “The book is cursed.” | Folklore | Historical events and stories of fires or war may be real; there is no verifiable evidence for a supernatural curse. |
What remains unknown
My assessment
🟢 Codex Gigas's “supernatural mystery” is largely legend.
The real mystery is not whether the Devil wrote the book. There is no historical evidence for that, and its physical production can be explained through ordinary medieval bookmaking.
The genuinely remarkable question is: why did a single scribe, or a very small production circle, create such an enormous and comprehensive codex in the thirteenth century? Its significance lies more in human labour and medieval knowledge culture than in the supernatural.
The Devil portrait alone is not evidence of a “satanic book”. Read alongside the facing Heavenly City, contrasts between good and evil, salvation and damnation offer a much more plausible context.
The work's history, contents and production context are fairly well known. Open questions concern the scribe's identity, the exact duration of production, missing leaves and the precise development of the legend.
References
The main framework draws on institutional catalogues and manuscript records; popular “curse” stories were not used as sources.
National Library of Sweden
Library of Congress record
Last updated: 6 October 2026.