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(CNN)A trio of codebreakers has found and deciphered a treasure trove of lost letters written by Mary, Queen of Scots.
The 57 secret letters, from Mary Stuart to the French ambassador to England between 1578 and 1584, were written in an elaborate code. The findings come 436 years after Mary's death by execution on February 8, 1587.
Most of the letters were kept in the Bibliothèque Nationale de France in Paris, mainly in a large set of unmarked documents that were also written in cipher — special graphical symbols. The documents were listed as dating from the first half of the 16th century and thought to be related to Italy.
Then, a trio passionate about cracking historical ciphers stumbled upon the documents.
George Lasry, a computer scientist and cryptographer from France; Norbert Biermann, a pianist and music professor from Germany; and Satoshi Tomokiyo a physicist and patents expert from Japan, all worked together to find the truth behind the documents.
The multidisciplinary team has worked together for 10 years to find and understand historical ciphers. Lasry is also a member of the DECRYPT Project, which digitizes, transcribes and identifies the meaning of historical ciphers.
Once the researchers began working through the unique ciphers, they quickly realized the correspondence was written using French, and there was nothing Italian about it.
The team spied verbs and adverbs that used a feminine form, mentions of captivity — and a keyword: Walsingham. Sir Francis Walsingham was Queen Elizabeth I's secretary and spymaster. Together, all signs pointed to the fact that the team may have found letters of Mary Stuart thought lost for centuries.
The results were published Tuesday in the journal Cryptologia.
Mary Stuart's sophisticated ciphers protected her secret letters for centuries.
"Mary, Queen of Scots, has left an extensive corpus of letters held in various archives," Lasry said in a statement. "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 newly deciphered material, which is about 50,000 words total, sheds new light on Mary's time spent in captivity in England.
Secret correspondence
Mary Stuart, a Catholic, was first in line for the succession to the English throne after her Protestant cousin, Queen Elizabeth I. Catholics considered Mary as the rightful, legitimate sovereign. Considering Mary Stuart a threat, Elizabeth I imprisoned her cousin for 19 years, under the custody of the Earl of Shrewsbury in England for the majority of that time. She was executed by decapitation at the age of 44 for her alleged part in a plot to have Elizabeth I murdered.
But Mary wasn't idle in captivity. She maintained regular correspondence with allies and tried to recruit messengers to hide her letters from enemies.
The new letters reveal new details about her communication with Michel de Castelnau, sieur de la Mauvissière, the French ambassador to England. The correspondence may have started as early as 1578. The ambassador forwarded letters from Mary to her agents in France.