Archive · 2 Oct 2026
After 217 Years, AI Cracks Napoleon's Mysterious War Letter
A very old letter connected to Napoleon was written in a secret code.
It was sent in 1809 to one of his generals, Auguste de Marmont.
People could not understand most of the letter for 217 years.
Carter Church used an artificial intelligence system to study a picture of it.
The system read thousands of unusual marks and worked out the code in about six hours.
The message described where French and Austrian soldiers were moving.
It was written shortly before Austria invaded.
The letter also completes a sentence that Napoleon later began in his memoir.
A letter sent in 1809 to Auguste de Marmont had remained undeciphered for 217 years.
Carter Church used OpenAI's GPT-6 Astra to analyze an image and decode the letter in about six hours.
The letter contains details about French and Austrian troop movements before Austria invaded.
The system transcribed about 1,300 hand-drawn signs and used a simulated-annealing solver to crack the code.
The decoded text completes a sentence from Napoleon's 1865 memoir, referring to “a gathering of rabble.”
- Who
- Carter Church decoded a letter sent by Eugene, Napoleon's stepson, to Auguste de Marmont.
- What
- An artificial intelligence system decoded a 217-year-old cipher containing military information.
- When
- The letter was written in 1809, about two weeks before Austria invaded; it was decoded in approximately six hours.
- Where
- The letter concerned French and Austrian forces; its specific writing location is not stated.
- Why
- It was a war briefing about troop movements before war between France and the Habsburg Empire.
- Letter date
- 1809
- Time undeciphered
- 217 years
- Decoder
- Carter Church
- AI system
- OpenAI's GPT-6 Astra
- Decoding time
- Approximately six hours
- Signs transcribed
- About 1,300 hand-drawn signs
- Subject
- French and Austrian troop movements before Austria's invasion