Mary Queen of Scots’ lost letters: codebreakers crack secrets of her correspondence 430 years on

Letters written by Mary Queen of Scots while she was in captivity have been found and decoded - more than 430 years after the former Queen of Scotland wrote them.

Mary wrote the letters in code while she was imprisoned by her cousin, Queen Elizabeth I, and they were believed to be lost for centuries - until they were found in a library in France by an international team. They were able to use computerised and manual techniques to decode the letters - and the details have now been released to the public.

One of the 16th Century’s most famous figures, Mary was first in line of succession to the English throne - after her cousin Elizabeth. Catholics considered Mary to be the legitimate monarch, however, and so Elizabeth had her imprisoned for almost two decades because she saw her as a threat. Mary was then eventually killed in 1587 because of her alleged part in a plot to kill Elizabeth. While she was in captivity, she wrote of many issues including her poor health, challenges with maintaining links to the outside world and the negotiations she had with her cousin about her release.

So, what  exactly did the letters say, who were they sent to, who found them and who was Mary Queen of Scots? Here’s what you need to know.

What did Mary Queen of Scots’ letters say?

Mary’s letters, which were written between 1578 and 1584, reveal new insights into her time in captivity. She wrote of her distress when her son James, the future King James I of England, abducted in August 1582 and her feeling that they had been abandoned by France. Her mistrust of Elizabeth’s spymaster Sir Francis Walsingham was also apparent, as well as her animosity for Robert Dudley, Earl of Leicester and a favourite of Elizabeth.

Who were the letters sent to?

Most of Mary’s letters are addressed to Michel de Castelnau de Mauvissière, the French ambassador to England. He was a supporter of Catholic Mary who was under the Earl of Shrewsbury’s custody when she wrote them. She also communicated with her associates and allies through extensive efforts to recruit messengers and to maintain secrecy.

The existence of a confidential communication channel between Mary and Castelnau is well-known to historians, and even to the English government at the time. Dr Lasry and his fellow codebreakers’ discovery provides new evidence that this exchange was already happening as early as May 1578 and continued until at least mid-1584.

Who found Mary Queen of Scots’ letters?

The letters were found by accident. George Lasry, a computer scientist and cryptographer, Norbert Biermann, a pianist and music professor, and Satoshi Tomokiyo, a physicist and patents expert, found them while searching the national library of France’s online archives for enciphered documents, Bibliothèque nationale de France. The trio did not realise what they had found at first and only discovered Mary was the author after solving her highly sophisticated cipher system.

Dr Lasry and his colleagues said some of the letters were in a large set of unmarked documents in cipher and used the same set of graphical symbols. The Bibliothèque nationale de France catalogue listed them as coming from the first half of the 16th century, and said that they were about Italian matters.

Upon beginning their work the team "quickly realised" that they were written in French and "had nothing to do" with Italy. Their work then revealed several mentions of captivity, and the name Walsingham which raised the suspicion that they might have been written by Mary. This was then confirmed by comparing the newly discovered letters with the plaintext of letters in Walsingham’s papers in the British Library, and also through other methods. A search for similar letters in Bibliothèque nationale de France collections unearthed 57 letters with the same cipher.

Lead author Doctor Lasry said: “Upon deciphering the letters, I was very, very puzzled and it kind of felt surreal. We have broken secret codes from kings and queens previously, and they’re very interesting, but with Mary Queen of Scots it was remarkable as we had so many unpublished letters deciphered and because she is so famous.

“This is a truly exciting discovery. Together, the letters constitute a voluminous body of new primary material on Mary Stuart – about 50,000 words in total - shedding new light on some of her years of captivity in England. Mary, Queen of Scots, has left an extensive corpus of letters held in various archives. There was prior evidence, however, that other letters from Mary Stuart were missing from those collections, such as those referenced in other sources but not found elsewhere. The letters we have deciphered are most likely part of this lost secret correspondence.”

The team’s decipherment of 57 letters, which was published in the journal Cryptologia on the 436th anniversary of Mary’s execution, on 8 February 2023, reveals around 50 new scripts previously unknown to historians. Dr Lasry and his colleagues still believe that other enciphered letters from Mary which are known to have existed may still be missing.

Dr Lasry added: “In our paper, we only provide an initial interpretation and summaries of the letters. A deeper analysis by historians could result in a better understanding of Mary’s years in captivity. It would also be great, potentially, to work with historians to produce an edited book of her letters deciphered, annotated, and translated.”

Who was Mary Queen of Scots?

Mary Queen of Scots, who was also known as Mary Stuart or Mary I of Scotland, was the Queen of Scotland from 14 December 1542 until her forced abdication in 1567. She was six days old when her father, James V of Scotland, died in December 1542, and she inherited the throne.

Mary married James Hepburn, 4th Earl of Bothwell in May 1567, but there was an uprising against the couple as it was believed that Hepburn had been behind the death of Mary’s former husband, Henry Stuart, Lord Darnley, the year before. On 24 July 1567, Mary was forced then to abdicate in favour of her one-year-old son, James, who she had with Lord Darnley. She made an unsuccessful attempt to regain the throne, and then fled to the south in the hope of gaining the protection from her first cousin once removed, Elizabeth I of England.

Mary had once claimed Elizabeth’s throne as her own, as she was the great-granddaughter of Henry VII of England, and was considered the rightful monarch of England by many English Catholics. Elizabeth did not give Mary protection and, fearing she would be a threat to her seat on the throne, she instead had her confined.

After 19 years in prison, Mary was found guilty of plotting to assassinate Elizabeth in 1586. She was executed for her part in the plot, aged 44, at Fotheringhay Castle in Northamptonshire, on 8 February 1587.