AI Cracks 217-Year-Old Napoleonic Military Cipher in Hours

By Tahani Elghazaly
Published October 4, 2026

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Artificial intelligence has helped decode a 217-year-old encrypted military message from the Napoleonic era, revealing troop movements and strategic intelligence from the weeks leading up to France’s 1809 war with Austria.

The document dates to March 1809 and was issued from the headquarters of Eugène de Beauharnais, Napoleon Bonaparte’s stepson and Viceroy of Italy. It was intended for French Marshal Auguste de Marmont.

Although some reports have described it as a “Napoleon letter,” the document was not handwritten by Napoleon. Instead, it carried military information and instructions connected to the French emperor’s command.

AI and cybersecurity engineer Carter Church used an advanced artificial intelligence model to analyze an image of the encrypted document. The system completed the main decoding work in about six hours, combining symbol recognition, linguistic analysis and historical cross-checking.

The task was unusually complex. The letter contained roughly 1,300 coded units built from about 155 handwritten symbols, numbers and characters, while variations in handwriting made some symbols difficult to distinguish.

The cipher relied on a system known as homophonic substitution, in which several different symbols can represent the same letter. Some symbols could also stand for entire words, making conventional frequency analysis significantly less effective.

Only a limited number of symbols had previously been identified. The AI system used those known values as a starting point, then tested possible meanings for the remaining characters against French language patterns and historical documents from the same period.

Once reconstructed, the text revealed information about French and allied troop positions, Austrian military movements and the forces Napoleon expected to assemble as tensions escalated across Europe.

The message also reflected French expectations about possible Russian military activity, offering another glimpse into the strategic assumptions shaping Napoleon’s planning before fighting began.

The document had appeared in a French military publication in 1969 but was incorrectly dated to 1807. The reconstructed text and surrounding historical evidence helped place it in March 1809, shortly before Austria launched its offensive against Bavaria.

The importance of the breakthrough extends beyond the content of the message itself. The experiment demonstrates how artificial intelligence can assist historians in reading difficult archival material, distinguishing handwritten symbols and reconstructing incomplete cipher systems.

Church later published details of the decoding process, along with the reconstructed text, cipher key and supporting material used to verify the result, allowing the method to be examined and independently tested.