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Long-lost secret letters of Mary, Queen of Scots, have just been decoded

This illustration, scanned from an original 1830s print, was engraved by W Holl and is titled "Mary Queen of Scots," from the original by Sir John Watson Gordon. (iStock)
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A trove of long-lost letters written in code by Mary, Queen of Scots, has been discovered and deciphered by an international team of codebreakers. Mary Stuart, who was first in line to succeed Queen Elizabeth I of England, wrote the letters during nearly two decades of imprisonment by Elizabeth that led to her beheading 436 years ago Wednesday, on Feb. 8, 1587.

Considered by Catholics to be the true sovereign of England, Mary was held under guard for 19 years by her cousin — the Protestant daughter of King Henry VIII — for fear that she was plotting against the throne. While in captivity, Mary wrote letters in code to allies and associates in an attempt to gain her freedom and become queen.

Some of that correspondence, now in the British National Archives, was intercepted and deciphered by Elizabeth’s secret agents. It was used as evidence of a plot to overthrow the crown and led to Mary’s execution.

The other letters were believed lost to history — until George Lasry, a French computer scientist and cryptographer; Norbert Biermann, a German pianist and music professor; and Satoshi Tomokiyo, a Japanese physicist and patents expert, found them in the online archives for enciphered documents at Bibliothèque nationale de France, the country’s national archives.

The trio, which released its findings Wednesday, used a computer algorithm to break about 30 percent of the code. They then had to resort to manual decryption to understand the rest of the letters, which included a series of symbols representing certain words.

“This is like solving a very large crossword puzzle,” Lasry told CNN. “Most of the effort was spent on transcribing the ciphered letters (150,000 symbols in total), and interpreting them — 50,000 words, enough to fill a book.”

Most of the lost letters are written to Michel de Castelnau, Sieur de la Mauvissière, the French ambassador to England, who was a supporter of Mary. They include references to the conditions of her captivity, as well as complaints about her poor health and her negotiations with Elizabeth for her release, which she believed were not conducted in good faith.

“In our paper, we only provide an initial interpretation and summaries of the letters,” Lasry said in a statement. “A deeper analysis by historians could result in a better understanding of Mary’s years in captivity.”

The study, published in the peer-reviewed journal Cryptologia, details the discovery of the letters and the efforts to decode them. The cryptologists say there may be other missing letters written by Mary yet to be discovered.