An international team of codebreakers say they have found and deciphered the long-lost secret letters of 16th-century monarch Mary, Queen of Scots. The documents were found mislabelled in the digital archive of the French national library.

The missing letters, which were found mislabelled in the digital archive of a French library, were hailed by historians as the most significant discovery about the Scottish queen in a century.

Mary Stuart, a Catholic, wrote the coded letters between 1578 and 1584 while she was imprisoned in England because of the threat she was believed to pose to her Protestant cousin, Queen Elizabeth I.

Mary was beheaded in 1587 after being found guilty of plotting to assassinate Elizabeth.

Mary was, in fact, far from the minds of the three codebreakers who accidentally discovered more than 50 of her letters.

The three are members of the DECRYPT project, an international, cross-disciplinary team scouring the world’s archives to find coded historical documents which they then try to decipher.

The trio were trawling through the digitised archive of France’s national library, known as the BnF, when they stumbled onto enciphered documents labelled as being from Italy in the first half of the 16th century.

“If someone wanted to look for Mary Stuart material in the BnF, that’s the last place they would go,” said French computer scientist and cryptographer George Lasry, the lead author of a new study in the journal Cryptologia.

Lasry told the AFP news agency that deciphering the code “was like peeling an onion,” for the trio, which also includes German music professor Norbert Biermann and Japanese physicist Satoshi Tomokiyo.

The breakthrough word

First, the codebreakers realised the text was not in Italian, but French.

The writer also used feminine forms, indicating a woman. Phrases like “my liberty” and “my son” suggested it was an imprisoned mother.

Then came the breakthrough word: “Walsingham”.

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Francis Walsingham was Elizabeth I’s principal secretary and “spymaster”.

Some historians believe it was Walsingham who trapped Mary in 1586 into supporting the foiled Babington Plot to assassinate Queen Elizabeth I, Lasry said.

Most of Mary’s letters are addressed to Michel de Castelnau Mauvissiere, the French ambassador to England and a supporter of Mary.

Mary was “too smart” to mention any assassination plot in the newly unearthed letters, Lasry said.

Instead the letters show her diplomatically pleading her case, gossiping, complaining of illnesses and perceived antagonists, and expressing distress when her son, King James VI of Scotland, was abducted.

Sensation for historians

Historians have praised both the code breaking and historical skills of the trio, with professionals eager to get stuck into the letters themselves.

“This discovery is a literary and historical sensation,” said John Guy, the British historian who wrote a Mary Stuart biography on which a 2018 film starring Saoirse Ronan was based.

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Steven Reid, a Scottish history expert at Glasgow University, said it was “the largest discovery of new Marian evidence in the modern era”.

He told AFP it would probably lead to a revised version of Mary’s life, adding that the cipher could help produce more accurate versions of her other coded letters.

Some of Mary’s letters are still believed to be missing, with the researchers saying a physical inspection of the BnF’s undigitised stock of original documents could be the next place to turn.

Originally published on RFI