Emperor Charles V's secret code cracked after five centuries

A team of researchers have cracked a five century-old code that reveals a rumoured French plot to kill the Roman emperor and king of Spain Charles V.

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

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

The letter from Charles V to Jean de Saint-Mauris had languished forgotten for centuries in the collections of the Stanislas library in Nancy. Cécile Pierrot, a cryptographer from Loria laboratory, first heard of its existence at a dinner in 2019, and after much searching she was able to set eyes on it in 2021.

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

In another obstacle, he used meaningless symbols to mislead any adversary trying to decipher the message.

Another letter from Jean de Saint-Mauris, where the receiver had doodled a form of transcription code in the margin, also helped.