A secret letter handwritten by the young military strongman Napoleon Bonaparte has finally been deciphered after more than two centuries.
In March 1809, during the conflict between France and Austria, Napoleon’s stepson—Eugène de Beauharnais, then Viceroy of Italy—sent this letter to the French general Auguste de Marmont.
At the time, this close associate of Napoleon was commanding troops stationed in Dalmatia, on the eastern coast of the Adriatic Sea, completely cut off from other French forces and their allies.
The letter began in Napoleon’s native French, but the subsequent 24 lines consisted of a baffling mix of symbols, letters, and numbers.
Experts believe the original letter likely came with a decryption key, but that key had long been lost to history—until now.
Carter Church, an engineer at the cybersecurity firm SentinelOne, used artificial intelligence (AI) to crack a code that had remained unsolved for centuries.
“I used GPT-6 Astra to crack a code from General Napoleon that had gone unsolved for 217 years. What’s truly impressive isn’t just the cracking of the code itself, but that Astra completed the entire multimodal workflow—starting from just an image and a goal—in only six hours,” he explained on X.
The first line of the secret letter reads: “Vous avez dû recevoir, Monsieur le Général Marmont, mes lettres des 8, 14 et 20 courant,” which translates to: “General Marmont, you must have received my letters from the 8th, 14th, and 20th of this month.”
The rest of the encrypted letter remained a mystery until Church used AI to decode it over the course of six hours. The AI’s decoding revealed that the letter outlined the positions of all other French and allied forces, urged him not to lose hope or be intimidated by his isolated situation, and assured him that Austria was heading toward ruin.
“Russian troops are marching on Austria; the Army of Friuli has reached a strength of 80,000 men today,” the letter read. “Add to this the Army of Dalmatia—not to mention the reserves gathering in the rear—and Austria will immediately face attacks from all sides. Thus, she is hastening toward her own destruction.”
“When you receive the order to advance, do not be intimidated by small detachments or ragtag forces.”
He added, “I am still anxiously awaiting news from you.”
Just two months later, on May 21, 1809, at the Battle of Aspern-Essling near Vienna, Napoleon suffered his first personal battlefield defeat, resulting in the deaths of 23,000 French soldiers.