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Emperor Charles V often used codes in his letters to ambassadors across Europe. One written in 1547 to his representative in France has just been decoded.

Emperor Charles V's secret code is deciphered after nearly 500 years

Cryptographer Cecile Pierrot and historian Camille Desenclos have recently announced that they have cracked the code used by Emperor Charles V in letters to Jean de Saint-Mauris, his ambassador at the French court in 1547. The letter had been neglected for centuries in the basement of the Stanislas Library in Nancy, eastern France, before Pierrot heard of its existence. After tracking it down she set about decoding it. Instead of the few days that she expected, it was several months before the breakthrough was made when Desenclos shared another coded letter with the team. On this the recipient had jotted notes about how to read the message.

The letter was 3 pages long, with three sections in plain French and the rest encoded. The code was more complex than originally thought. Both simple and complex symbols were used, representing letters or a combination of letters. In addition, some symbols represented whole words or phrases, such as a needle for 'king of England', and diacritical marks (accent-like marks) were used for vowels, with the e vowel usually omitted. Some symbols had no meaning at all, included to confuse the untrained reader.

The Political and Diplomatic Background

Written in February 1547, a few weeks after the death of Henry VIII and only a month before that of Francis I, king of France, it provides an excellent example of the often tense political and diplomatic situation that prevailed for much of the sixteenth century. Although Emperor Charles and Francis I were officially at peace, having signed the Treaty of Crepy in September 1544, both were aware that their rival would take advantage of any weakness. The treaty 'in many ways reveals the nature of international politics at the time - sometimes laudable aims, often duplicitous agreements, and then an open disregard for what had been signed' (page 283, 'Charles V: Duty and Dynasty' by Richard Heath - 2018).

In early 1547 Charles was campaigning against the Protestant princes of the Schmalkaldic League in the Holy Roman Empire. He wanted to deter any support that France or England might provide to the League by giving the impression that he would undoubtedly be victorious. Charles wanted his ambassador to downplay the recent rebellion against him in Prague and also to find out as much as he could about a rumour of a plot to have him assassinated.

The necessity for the code was obvious. There was a one-in-two chance of such communications being intercepted by the French and some of the information needed to be kept secret. However, Charles also wished the French to be aware of other events that would make him look politically or militarily stronger. These were left in plain language, and although it would be clear to the French that Charles had done this deliberately, they would still have the task of deciding how reliable such information might be.

The world of 16th century foreign policy and diplomacy is investigated in my new book 'Henry VIII and Charles V: Rival Monarchs, Uneasy Allies', to be published by Pen and Sword in February 2023.

A 20% discount is available on pre-orders from the Pen and Sword website. www.pen-and-sword.co.uk/Henry-VIII and Charles V

Image: Bibliotheque Stanislas De Nancy

The Aftermath

Francis died on 31st March 1547, to be succeeded by his surviving son, Henri II. Charles defeated the Protestant princes at the battle of Muhlberg on 24th April 1547 but his victory did not bring about the religious settlement that he had wanted. The new French ruler was to be just as hostile to the emperor as his father had been and in 1552 an alliance of Henri II and the German Protestant leaders created more problems for the emperor. Although there may well have been plans for an assassination, this attempt on Charles's life was never made. After abdicating his titles during 1555 and 1556, he died peacefully at the monastery of Yuste, Extremadura, Spain, on 21st September 1558.

Full details of the code, how it was broken, and a full translation of the letter, will be presented in an academic paper by the team. It is hoped that more such letters will come to light and can be used to gain a greater understanding of Emperor Charles V's political and diplomatic manoeuvring during his lengthy reign.

Richard Heath
Richard Heath
Richard Heath graduated in history from the University of Cambridge and was a history teacher for 35 years. He now enjoys travelling with his wife in their VW camper van, exploring historical sites and appreciating all that Europe has to offer.

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