Codes and Crowns

The letters date from 1578-84 and are mostly from Mary to Michel de Castelnau, Sieur de la Mauvissière, the French ambassador to England. Ciphers generally disguised each letter with a single symbol, but to enhance security homophones were used - that is, multiple symbols could be used to represent the most common letters. The contents of these letters are a mix of political discussion and personal complaint, a theme we see across Mary's letters. Rather than offering salacious new information then, these letters are more informative about how Mary maintained links with supporters even during the intense surveillance of her imprisonment. The new letters have also helped to confirm a long-held suspicion that there was a mole in the French embassy who successfully passed letters to the English. The numerous letters from 1582-83 on the other hand suggest that a reliable route of transmission had been established and the survival of both ciphered letters and contemporary plaintext copies in English archives indicates the success of the mole throughout 1584. Code names for prominent figures and letter-bearers that have been identified here could also be applied to more of Mary's letters, revealing new details.