A team of researchers have cracked a five-century-old code which reveals a rumoured French plot to kill the Holy Roman Emperor who was also 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 t…