AI decodes 217-year-old Napoleonic letter in 6 hours
An engineer used artificial intelligence to decode a military cypher from the Napoleonic era that had gone unsolved for more than two centuries.
Artificial intelligence has successfully decoded a 217-year-old letter written in 1809, a feat achieved in just six hours. The document, written by Eugène de Beauharnais on Napoleon Bonaparte's orders, was an encrypted troop briefing meant for French General Auguste de Marmont. The AI model, OpenAI's GPT-6 Astra, transcribed the image, transcribed the image, analyzed the homophonic substitution cipher, wrote code, and cross-referenced historical records to break the cipher.
The letter revealed the positions of Bavarian, Polish, and French forces, showing that Austria was preparing to attack France while French forces were still engaged in Spain. Napoleon had ordered the message to be written in cipher and carried by a reliable officer, warning that Austria would be attacked on all sides if Russia marched against them.
The decoded information helped officers understand troop numbers, titles, and unit positions, ultimately leading Church to redate the document to late March 1809, two weeks before Austrian forces launched their offensive. The complete research, including the transcription, cypher tables, and scripts, was published on September 18, with Satoshi Tomokiyo of Cryptiana confirming the solution.
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