What is the letter to Marmont?

A ciphered letter sent in late March 1809 to General Auguste de Marmont, then commanding about 13,000 French troops in Dalmatia. Written on Napoleon's order of 16 March, it gave the position of every French and allied army two weeks before Austria invaded Bavaria.

Why could nobody read the letter for 217 years?

Its key was lost, it used a homophonic cipher that defeats simple letter counting, and the only known copy is a single reproduction printed in a French army journal in 1969 under the wrong date. For decades it sat on lists of unsolved historical ciphers.

What is a homophonic cipher?

A substitution cipher in which frequent letters have several interchangeable signs, so the frequencies that usually betray a cipher are flattened. In the Marmont letter the letter E alone has nine signs, and 29 further signs stand for whole words such as de, que and vous.

Who decoded the letter to Marmont?

Carter Church, who had never broken a cipher before, decoded it in September 2026 from one scanned page, working with an AI model. He built on 33 letter values already published by the French historian of cryptography Daniel Tant, and published the full key and verification files.

What does the decoded letter say?

It lists the French and allied armies Napoleon named in his order, from Lefebvre's 40,000 Bavarians at Munich to Oudinot's elite corps on the Lech, then adds where the Austrians were gathering, at Laibach, Klagenfurt, Villach and Salzburg, and urges Marmont not to be intimidated.

Were the letter's predictions correct?

Partly. The Austrian positions were right: Austria invaded Bavaria and Italy from those places on 10 April 1809. The claim that the Russians were marching on Austria was propaganda Napoleon had ordered spread, and Russian troops crossed into Galicia only on 3 June.

What words were missing from Napoleon's printed orders?

The 1865 edition of Napoleon's correspondence breaks off at 'a handful of' followed by a row of dots. The cipher letter, written from the same order, reads 'un rassemblement de canailles', a gathering of rabble. It paraphrases the order, so it is evidence of the missing words, not proof.

How can I read an old family document nobody understands?

Start from what you already know, such as a name, date or place, and test each reading against the whole page rather than one word. Then compare it with a second record. On Vestigee you can upload the document, read the handwriting, translate it and attach each name to your tree.

Vestigee — The Letter to Marmont: A Napoleonic Cipher, Read at Last | Blog

In 1809, Napoleon ordered a ciphered letter for General Marmont. Nobody could read it for 217 years. Here is what it says, and how it was finally decoded.