Artificial intelligence decodes Napoleon Bonaparte's secret military correspondence

Carter Church, a cybersecurity engineer at SentinelOne, used an artificial intelligence model to decode a secret letter from Napoleon Bonaparte.

The letter was originally sent in March 1809 to the officer Auguste de Marmont regarding troop positions in Dalmatia, a region in modern-day Croatia. Napoleon ordered the message to be encrypted to prevent the Habsburg Empire from intercepting his military plans. The message remained unreadable for 217 years because the specific key used to encrypt it was lost.

While human cryptographers had previously decoded 33 symbols within the text, the full content remained a mystery. Church utilized the GPT-6 Astra model from OpenAI to process the 1300 characters, which consist of 155 different symbols including numbers, letters, and invented signs. The AI spent six hours calculating the solution. To solve the puzzle, the AI used a method called simulated annealing.

This process compares trial-and-error solutions against statistics of letter frequencies in French literature from that era and previous letters from Marmont. The system discovered that some symbols represented entire words rather than single letters. The decoded text reveals Napoleon's specific troop locations, including 40,000 Bavarian soldiers near Munich or Passau and an elite corps near Augsburg.