Mary, Queen of Scots' Lost Letters

Summary

Cipher letters filed in the French national library as Italian papers were in fact written by Mary, Queen of Scots, as a prisoner in England. Three codebreakers broke the cipher and published the letters in 2023: about 50,000 words written between 1578 and 1584, mostly to the French ambassador in London.

The letters were never lost in the ordinary sense. They sat, catalogued, in the national library in Paris. What was missing was anyone who knew what they were, or could read them.

What is documented

The find. George Lasry, a computer scientist and cryptographer, Norbert Biermann, a pianist and music professor, and Satoshi Tomokiyo, a physicist and patents expert, found the letters in the online archives of the Bibliothèque nationale de France. Lasry is part of DECRYPT, a project involving several European universities that maps, digitises, transcribes and deciphers historical ciphers. Some were in a large set of unmarked documents written entirely in cipher, all using the same set of graphical symbols. According to the publisher, the library's catalogue listed them as "from the first half of the 16th century, and related to Italian matters".

The break. Using a combination of computerised and manual methods, the three broke the cipher. The plaintext was French and, in the publisher's summary, "had nothing to do with Italy". Verbs and adverbs in the feminine form, repeated mentions of captivity and the name Walsingham suggested the writer was Mary. Comparison with the plaintext of letters among Sir Francis Walsingham's papers in the British Library confirmed it.

The letters. The paper's abstract describes over 55 letters fully in cipher, about 50,000 words in all; the publisher's announcement counts 57 letters, about 50 of them previously unknown to historians. They were written between 1578 and 1584 and addressed mostly to Michel de Castelnau, seigneur de Mauvissière, the French ambassador to England.

What they say. Mary complains about her health and the conditions of her captivity, discusses negotiations with Elizabeth I for her release, and writes with mistrust of Walsingham and hostility towards Robert Dudley, Earl of Leicester. She expresses distress when her son James, already King James VI of Scotland and the future James I of England, is abducted in August 1582, and a sense of having been abandoned by France. She also writes about her keeper, the Earl of Shrewsbury.

The channel. Historians knew that Mary had kept a secret correspondence with the French embassy. The historian John Bossy wrote in Under the Molehill that, before it was compromised in mid-1583, it was "kept so secure that none of it has survived, and we don't know what it was". The deciphered letters are most likely part of that correspondence. They show that the channel was already in use by May 1578 and active until at least mid-1584.

The dates. Mary was executed at Fotheringhay Castle on 8 February 1587, after nearly nineteen years as a prisoner in England. The decipherment was published in the journal Cryptologia on 8 February 2023, 436 years to the day later, as an open-access paper of just over 100 pages.

Leading explanations

Letters of Mary, Queen of Scots, to the French embassy. Established. The attribution rests on internal evidence (the feminine grammar, the captivity, the people named), on external evidence (matches with plaintext copies in Walsingham's papers), and on a single consistent cipher across the set. It was published in a peer-reviewed journal.

Their historical significance. Still being assessed. The authors present the letters as new primary material on Mary's years of captivity and suggest that deeper analysis by historians could give a better understanding of that period. They hope to produce, with historians, an edited, annotated and translated edition. They also suggest that other enciphered letters from Mary, known to have existed, may still be missing.

Current status

Later explained. The letters have been identified, deciphered and published, and their attribution to Mary is established. Nothing in the record suggests it will be revised.

What remains is the historians' work: reading about 50,000 words of new material against what was already known of her captivity, and looking for the enciphered letters that are known to have existed but have not yet been found. Any further finds would be added to this record.

Last reviewed: September 2026. Records are provisional. Where the evidence changes, the entry changes. Found an error? Tell us.