AI helps decode a 217-year-old message sent on Napoleon’s orders

A 217-year-old military message sent on Napoleon’s orders has been deciphered with artificial intelligence, according to engineer Carter Church. The result makes a long-unresolved document readable and offers a detailed glimpse of preparations for war in 1809.

The letter came from the headquarters of Napoleon’s stepson, Eugène de Beauharnais, and was addressed to General Auguste de Marmont in Dalmatia, in present-day Croatia. It outlined French and allied troop positions and urged Marmont not to be intimidated by his isolation from other forces.

Church started with a single scan published in a French military journal in 1969. Beneath one readable line were 24 rows of numbers, letters and symbols. Building on earlier researchers’ work identifying 33 of the characters, the AI transcribed the message and wrote a program to test possible meanings against French language patterns. Church said the process took about six hours.

He published the transcription, code tables and scripts so others could reproduce the work. According to Church, cipher researcher Satoshi Tomokiyo reviewed the solution and marked the record as solved.

Church stressed that the cipher was not beyond human experts. The advance was bringing together the painstaking tasks of reading, organising and decoding the symbols, work that might otherwise remain undone.