DALMATIA — Carter Church, an engineer at the cybersecurity firm SentinelOne, used an AI model called GPT-6 Astra to decode a letter from 1809. The message was originally sent by Eugène, Napoleon's stepson and the Viceroy of Italy, to French General Auguste de Marmont.

"I used GPT–6 Astra to break an unsolved cipher to one of Napoleon’s generals that had gone unread for 217 years. What makes this impressive isn’t actually the codebreaking, but that Astra completed the entire multi-modal workflow in six hours from a single image and goal," Church said. The AI model processed the decryption in six hours using just one image and a prompt.

The AI leveraged a partial decryption table created by cryptology historian Daniel Tant, which identified 33 of the symbols. "The cipher itself isn’t difficult, and cryptographers could have cracked this easily given the time/energy, but the work to transcribe, catalog, translate, then crack is involved and multi-disciplinary," he said.

The letter's first line reads: "Vous avez dû recevoir, Monsieur le Général Marmont, mes lettres des 8, 14 et 20 courant." In English, this translates to: "You must have received, General Marmont, my letters of the 8th, 14th, and 20th of this month." It stated that Russian forces were advancing against Austria and that the army in Friuli then included eighty thousand men. The document added: "Add the Dalmatian corps, without counting the reserves being organized everywhere in the rear, and you see that Austria will be attacked at once on every side. She is consequently hastening toward her ruin." It also said: "When you receive the order to march, you must not allow yourself to be intimidated by a few troops or a gathering of rabble." The letter concluded: "I continue to await news from you with impatience."

"The takeaway here is that the people shortening those lists will increasingly be outsiders who were simply curious," he said. Napoleon faced his first personal defeat at the Battle of Aspern-Essling near Vienna on May 21, 1809. That battle resulted in the loss of 23,000 French soldiers.

Napoleon later defeated Archduke Charles at the Battle of Wagram in July 1809. The outcome of the Battle of Wagram led to the end of the Fifth Coalition, an alliance led by Austria and Britain against France.

What's New

A study titled Carter, Sir Ronald (Powell), (born 1935), consulting engineer, 2002–2016 was published in 2014 in Who's Who. The letter contained 1,300 signs made up of 155 distinct symbols, encoded using a homophonic cipher. Before this effort, the only publicly available image of the letter was a low-resolution scan published in a French army journal in 1969. The AI used a partial decryption table developed by cryptology historian Daniel Tant, which covered 33 of the symbols.

Why It Matters

The result highlights how AI can manage complex, multi-disciplinary tasks more efficiently than traditional methods, not just solve ciphers. It suggests that progress in decoding historical texts may increasingly come from non-specialists driven by curiosity.