AI engineer Carter Church used OpenAI’s GPT-6 Astra system to decode a 217-year-old encrypted letter from Napoleon Bonaparte to General Auguste de Marmont. The letter, sent by Eugène, Napoleon's stepson in 1809, detailed troop movements and instructed Marmont not to be intimidated by Austrian forces. GPT-6 Astra spent six hours decrypting the message using a technique called "simulated annealing," which involves trial and error to find matching words. This breakthrough showcases AI’s capability in deciphering complex codes, though it raises concerns about privacy and anonymity online.
Written locally by qwen2.5:14b on 2026-10-01,
using this article's own text rather than the other coverage of the
same event (that is the story summary below).
Story summary
Carter Church, an AI engineer at SentinelOne, successfully decrypted a coded message from Napoleon Bonaparte to his general Auguste de Marmont using OpenAI’s GPT-6 Astra system after 217 years. The letter, sent by Napoleon's stepson Eugène, contained details about French and Austrian troop movements on the eve of war between France and the Habsburg Empire in 1809. The ciphered note had 1300 characters, including letters and symbols, and was a mystery until GPT-6 Astra transcribed it within six hours by employing simulated annealing techniques. This breakthrough highlights the potential of AI in solving complex historical puzzles beyond human capabilities.
Written for “Napoleon Code Cracked” on 2026-10-05,
grounded in this article and the 1 other(s) covering the same event.
A coded letter carrying a message from Napoleon Bonaparte to one of his senior generals has been cracked by AI after 217 years.
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letter → cod → years
The contents of the letter, sent by Eugène, Napoleon’s stepson, on the emperor’s instructions, had remained a mystery since it was sent to Auguste de Marmont in 1809.
However, Carter Church, an AI engineer at cybersecurity company SentinelOne, said this week he had used OpenAI’s GPT-6 Astra system to decrypt and transcribe the message for the first time.
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he → send → time
The letter contained details of French and Austrian troop movements on the eve of war between France and the Habsburg Empire.
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letter → contain → France
The note contained 1300 characters, some of which represented letters and other old words.
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some → contain → letters
The cipher to decrypt the message has been lost, meaning the letter’s contents have been unknown for more than two centuries.
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contents → decrypt → centuries
GPT-6 Astra – an advanced version of the AI system that powers ChatGPT – spent six hours transcribing the characters and mapping them against work from cryptographers that had solved 33 of the characters.
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that → power → characters
It then decoded the message using a technique known as “simulated annealing”, a process of trial and error in which multiple candidate words are tried to see whether they fit, and compared them to Marmont’s existing writing.
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they → decode → writing
While the process could have been done by hand, it would have been a laborious process that no cryptographer to date has accomplished.
uncertain
cryptographer → do → date
Church said he had never attempted to decode a cipher before but had been inspired to after seeing an AI model decode a 1941 German army message.
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model → say → message
In that case, Carter Leffen, another tech developer, simply told the GPT-6 Astra AI tool to find and decrypt an unsolved Enigma message, which it managed in around 10 hours.
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it → tell → hours
Recently released AI models have been found to be highly capable of solving mathematical problems as well as deciphering code.
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models → release → code
Decrypting ciphers often involves painstaking work of patching together multiple possible combinations of words, something that AI systems can do much more quickly than humans.
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systems → decrypt → humans
Researchers have raised concerns that the same capabilities will be used to unmask anonymous online profiles, by matching their writing patterns and other identifiers with real people.
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capabilities → raise → people
The letter to General Marmont, who was stationed in modern-day Croatia and separated from Napoleon’s main armies, came as the Habsburgs prepared for war with France to regain lost territory.
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Habsburgs → station → territory
It contains details of the locations and strength of the French and Austrian forces and instructs him to prepare to march and not be “intimidated by a few troops or a gathering of rabble”.
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It → contain → rabble
The letter adds: “Austria will be attacked at once on every side.
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Austria → add → side
She is consequently hastening towards her ruin.”
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She → hasten → ruin
Marmont’s army was ultimately able to break out of Croatia and help Napoleon defeat Austria at the Battle of Wagram.
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Napoleon → break → Wagram
Marmont was made a Marshal, a rank awarded to his senior generals.
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Marmont → make → generals
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Telegraph → get → newsletter
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