After 217 years... AI deciphers secret message sent by Napoleon's order

An engineer at a cybersecurity firm has successfully decrypted a military message from 1809, sent to French General Auguste de Marmont by order of Napoleon Bonaparte, after its contents remained unreadable for 217 years.

According to a report published by engineer Carter Church of Sentinel One, Napoleon wrote from Paris on March 16, 1809, to his adopted son Eugène de Beauharnais, Viceroy of Italy, requesting that he send a coded message to Marmont containing the positions of French armies and their allied forces.

Church explained that he used OpenAI’s “GPT-6 Astra” artificial intelligence model to decrypt the message, a process that took approximately six hours and started from a single image of the document.

The document consists of an initial line written in French, followed by 24 lines of encrypted text containing two-digit numbers, letters, and handwritten symbols. The original decryption key, which would have allowed the message to be read, is no longer available.

According to Church, the message contains approximately 1,300 encrypted units and 155 distinct symbols. Only 33 values were known from a partial key, requiring the deduction of the remaining cipher based on the message’s content itself.

The model handled the transcription, analysis, and decryption of the document. It divided the image into rows, read the symbols, and identified which of the 175 hand-drawn symbols represented the same character despite variations in handwriting, before proceeding to analyze the cipher and compare the results with historical records.

The decrypted text revealed a military briefing detailing the positions and numbers of several French and allied forces prior to the war with Austria. It also included a message intended to reassure Marmont, whose troops were stationed in Dalmatia and isolated from the rest of the French armies by Austrian territory.

The message noted the movement of Russian forces against Austria, stated that the Army of Friuli comprised 80,000 men, and mentioned forces in Dalmatia and reserves being organized behind the front lines.

It also instructed Marmont not to be intimidated by the forces he faced, as Napoleon expected Austria to come under military pressure from multiple fronts.

The document had been known since a copy was published in 1969 in the French military history journal *Revue Historique de l’Armée*. Its date had previously been attributed to 1807, but the decryption and comparison with Napoleon’s historical correspondence established that it dates to late March 1809.

Church published the details of the decryption process and its results. Satoshi Tomokyo, who manages the Cryptiana database of historical ciphers, reviewed the solution and logged the message as solved, according to Church. The decryption results were also covered by media outlets including Euronews and Live Science.