Secret letters written by Mary Queen of Scots while she was incarcerated by Queen Elizabeth I have been cracked by a team of codebreakers.
For centuries, the contents of coded communications from 1578 to 1584 were thought to have been lost.
Mary, who was beheaded on this day 436 years ago, used a complex code system to hide messages about her that codebreakers found included musings on her time in prison, failing health and attempts to negotiate her release.
Why was she put in jail?
Mary had been held in Scotland when she was detained in England – over a period of 19 years her incarceration was spread across castles from Carlisle to Fothering Sea.
The newly deciphered letter was written while she was in the custody of the Earl of Shrewsbury.
She was imprisoned by her cousin Elizabeth because she was considered a threat to her power.
Catholics consider Mary the rightful monarch and the first in line.
Ultimately, she was executed in 1587 at the age of 44 for her part in an alleged plot to kill Elizabeth.
What are these letters about?
Most of Marie’s letters were addressed to the French ambassador to England, Michel de Castelneau de Movisier, who supported her succession to the throne.
These included complaints about her poor health and conditions of captivity, as well as her distrust and contempt for Elizabeth’s chief secretary, Sir Francis Walsingham, and Robert Dudley, Earl of Leicester.
She also mourned the kidnapping of her son James (the future king) in August 1582.
Mary was known to have contacted allies while in prison – but the letters range from 1578 to 1584, suggesting they were sent both earlier and later than previously thought.
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The letters took some time to decipher. Image: George Lasry/Norbert Biermann/Satoshi Tomokiyo
How are they decoded?
The team, composed of computer scientist and cryptographer Georges Lasry, music professor Norbert Biermann and physicist Tomoyo Tomosei, stumbled upon 57 letters in the online archives of the Bibliothèque Nationale de France.
The library lists them as first half 16th century and related to Italian affairs – but the author soon realized they were written in French.
Cipher and Nomenclature Homonyms – This means that each letter of the alphabet can be encoded using more than one cipher symbol, ensuring that no one symbol appears too often.
Certain words, names, and places also have dedicated symbols.
Codebreakers have found some codes that represent whole words. Image: George Lasry/Norbert Biermann/Satoshi Tomokiyo
“The code was so complex that it took us a while to crack it,” said Mr Lasli of the University of Kassel.
“But after a while, we start to see some specious fragments of French texts. From these fragments, it can be seen that this writer is imprisoned, has a son, and is a woman, and can be compared with Mary Stuart.”
Their work reveals verbs and adverbs often in the feminine form, mentions captivity, and mentions Walsingham – described as “the final clue”.
This was confirmed by comparing them to the plaintext letters in the Walsingham Papers at the British Library – and managed to reveal dozens of scripts previously unknown to historians.
Their findings have been published in the peer-reviewed journal Cryptologia.
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Image: George Lasry/Norbert Biermann/Satoshi Tomokiyo
“Historic sensation”
The discovery was welcomed by leading expert John Gay, whose 2004 biography of Marie led to a 2018 film starring Saoirse Ronan and Margot Robbie.
“This discovery was a literary and historical sensation,” he said.
“This is the most important new discovery about Mary Queen of Scots in 100 years. I’ve always wondered if de Castelnaud’s original will one day come out – buried in the Bibliothèque Nationale de France or elsewhere – and cannot be found due to encryption identify.
“Now they have.”