AI Decodes Napoleon’s 1809 Military Cipher in Six Hours

GPT-6 Astra has reportedly deciphered a coded 1809 military briefing in about six hours, but the letter was not written by Napoleon himself. It originated with Eugène de Beauharnais, Viceroy of Italy, and was sent to General Auguste de Marmont on Napoleon’s orders, carrying information about French and allied forces.The account of the decoding

The hard part was more than breaking the code

Carter Church, an engineer at cybersecurity company SentinelOne, said the model worked from an image of the letter and handled a chain of tasks: dividing the page into rows, identifying repeated handwritten signs, transcribing them, analyzing the cipher, writing code and checking historical records. Church reported that the end-to-end work took roughly six hours.His account of the workflow and timing

The letter used a homophonic substitution cipher, in which a letter can be represented by multiple symbols. Live Science reports that GPT-6 Astra also found a previously known partial symbol table covering 33 symbols and applied it to the document.The reported cipher and partial table That detail matters: this was not simply a model guessing plaintext from an image. The solution drew on earlier cryptographic work and historical context as well as image processing.

Marmont was stationed in Dalmatia, and the briefing described the positions of French and allied forces. It urged him not to be intimidated when ordered to march and said the army of Friuli numbered 80,000. That number is a claim in the decoded letter, not an independently confirmed troop count.The letter’s reported contents

A decipherment, not a major new revelation

The message’s historical value is more measured than the dramatic age of the cipher suggests. Live Science reports that much of its content repeated information available in Napoleon’s other correspondence, which gave historians context for assessing the proposed reading. Historian Zack White also noted a discrepancy: the letter’s claimed force total was 60,000 above the troops Napoleon actually had available to fight, according to his account.The historical context and troop-number qualification

That context cuts both ways. It helps make the result testable, but limits the claim that the model uncovered an entirely unknown account of Napoleon’s plans. The decoded message also raises questions about the assumptions behind its troop figures and the emperor’s outlook before the campaign against Austria.

Church published a research record with the transcription, cipher tables and scripts, and Cryptiana researcher Satoshi Tomokiyo reviewed the solution and marked the cipher “solved,” according to Euronews.The materials and review Church said the cipher itself was not especially difficult for cryptographers; the labor lay in transcription and the cross-disciplinary work around it.Church’s assessment of the work

The useful signal is therefore less that AI has independently settled an obscure historical mystery than that it can help move a multi-step research task along when evidence exists to check the answer. Here, a proposed solution could be compared with surviving correspondence, historical details and a reproducible record. A different cipher without those supports would be a harder test.