The secret code of Emperor Charles V has been cracked after five centuries | Spain

A team of researchers has cracked a five-century-old code that reveals a highly publicized French plot to assassinate the Roman Emperor and King of Spain, Charles V.

Charles was one of the most powerful men of the 16th century, leading a vast empire that took over much of Western Europe and the Americas during a reign of more than 40 years.

It took the team at the Loria research lab in eastern France six months to decipher the letter, written in 1547 by the emperor to his ambassador to France. The tumultuous period saw a succession of wars and tensions between Spain and France, then ruled by Francis I, the Renaissance ruler who brought Leonardo da Vinci from Italy.

Charles V’s letter to Jean de Saint-Mauris had been forgotten for centuries in the collections of the Stanislas Library in Nancy. Cécile Pierrot, a cryptographer from the Loria lab, first learned of its existence at a dinner party in 2019, and after a long search, she was able to see it in 2021.

With the signature of Charles V, it was at once mysterious and completely incomprehensible, she told reporters on Wednesday.

Cécile Pierrot (L) and senior lecturer in modern history Camille Desenclos (R) explain the decoding process of a coded letter from Charles V.
Cécile Pierrot (L) and senior lecturer in modern history Camille Desenclos (R) explain the decoding process of a coded letter from Charles V. Photo: Jean-Christophe Verhaegen/AFP/Getty Images

In painstaking work, aided by computers, Pierrot found “separate families” of about 120 symbols used by Charles V. “Whole words are encoded with a single symbol,” and the emperor replaced vowels that came after consonants with signs, she said, an inspiration likely coming from Arabic.

In another obstacle, he used meaningless symbols to deceive any opponent who tried to decipher the message.

The breakthrough came in June when Pierrot managed to discern a sentence in the letter and the team then cracked the code with the help of Camille Desenclos, a historian. “It was a painstaking and lengthy work, but there was really a breakthrough that happened in one day where all of a sudden we had the right hypothesis,” she said.

Another letter from Jean de Saint-Mauris, in which the recipient had scribbled some form of transcription code in the margin, also helped.

Desenclos said it was “rare for a historian to read a letter that no one had read for five centuries”. It “confirms the somewhat degenerate state” in 1547 of relations between Francis I and Charles V, who had signed a peace treaty three years earlier, she said.

Relations between the two were strained, with several attempts to weaken each other. So much so that one piece of information that was revealed was the rumor of an assassination plot against Charles V that was allegedly brewing in France, Desenclos said. “Not much was known” about the plot, but it underscored the monarch’s fears, she said.

The researchers now hope to identify other letters between the emperor and his ambassador, “to have a snapshot of Charles V’s strategy in Europe”.

“It is likely that we will make many more discoveries in the coming years,” Desenclos added.

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