An artificial intelligence model has successfully decoded a 217-year-old military letter sent to one of Napoleon Bonaparte’s generals. The tool processed the unread dispatch in about six hours, revealing previously missing details about troop movements and political pressures leading up to the 1809 war against Austria.
Computational Efforts Unlock Complex Homophonic Cipher
The document was previously known only from a reproduction in a 1969 French military journal where it was mistakenly dated to 1807.
The physical record consisted of a single introductory line in plain text followed by 24 lines containing 1,300 cryptographic elements and 155 distinct symbols. Because the cipher was homophonic—meaning multiple symbols could represent the same letter—traditional frequency analysis proved difficult. Prior to recent computational efforts, cryptography historian Daniel Tant had identified the values of 33 symbols, unlocking about a third of the message, but 865 elements remained unread.
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How the GPT-6 Astra Model Tackled the 1,300-Sign Cipher
The software divided the scan into individual lines, cataloged handwritten signs, and matched varying styles of penmanship. It also relied on works by Victor Hugo, Alexandre Dumas, and Marmont’s memoirs, alongside specialized algorithms.
New Historical Details Recovered From Napoleon’s Correspondence
The newly readable text filled a notable gap in the published correspondence of the French emperor. In official print records, an order from March 16 breaks off abruptly. The newly decoded dispatch clarifies the phrasing, instructing the general not to succumb to pressure from several detachments or a crowd
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Napoleon urged Marmont, whose forces were stationed in Dalmatia and separated from the main armies, to maintain his composure despite his isolated geographic position across the Adriatic Sea among the territories of the Austrian Empire. The letter concluded with a direct assessment of the opposing strategy: Austria will be attacked immediately from all sides.
According to the decoded text of the 1809 military letter via ForkLog, Austria will be attacked immediately from all sides.
AI Model Decodes Unsolved Enigma Radio Message
The successful decipherment follows a similar project in September, when the same AI model was used to recover the key and text of an unsolved 1941 German Enigma radio message from the CryptoCellar archive that had baffled researchers for about 20 years. That effort was inspired after developer Carter Leffen asked the tool to find and decode an unsolved Enigma message, a task completed in about ten hours. While the technology demonstrates an ability to accelerate humanities and archival research, it has also raised discussions among researchers regarding digital security.