Napoleon’s 200-year-old mysterious letter deciphered using artificial intelligence

In 1809, while preparing for war with Austria, Napoleon Bonaparte sent a coded letter to General Auguste de Marmont. Because the cipher key had not survived, the letter's contents remained unknown for over two centuries.
AI engineer Carter Church discovered a copy of the letter, which had been published in a French military journal in 1969. He analyzed the letter using GPT-6 Astra. The neural network deciphered the code in approximately six hours by identifying 175 handwritten characters and testing various possibilities for the unknown symbols.
The reconstructed letter revealed that Napoleon was informing Marmont about the positioning and size of French troops, as well as a potential Austrian attack. Napoleon urged the general—who was cut off from the main army—not to fear the enemy. The letter was written using a homophonic cipher, in which multiple distinct symbols were used to represent a single letter. Thirty-three of the symbols were already known, while the rest were identified with the help of AI.
The researcher noted that some symbols may still have multiple possible meanings. Nevertheless, these uncertainties do not alter the general content of the letter. The reconstructed text, the cipher key, and the software used have also been made public.