I have used GPT-6 Astra to decipher two Catholic League letters from 1593, written by Thibault Desportes, the secretary to the Duke of Mayenne. To my knowledge, these letters have never been deciphered before. Desportes wrote these letters to Pope Clement VIII's nephew Pietro Aldobrandini (who was responsible for French affairs in Rome) and to Mayenne's agent in Rome, Girolamo Frachetta, just as Mayenne's war against the Protestant French king Henry IV was beginning to unravel. The letters were written 3 days before Henry converted to Catholicism in a bid to be recognized as the rightful ruler of France by the Pope and the French nobility. (You may have heard the expression "Paris is well worthy of a Mass", which Henry allegedly offered as the reason for his conversion.) In these letters, Desportes accuses the Pope of favoring Spanish interests over those of France and explains why a truce between the Catholic League (headed by Mayenne) and Henry IV would become inevitable following Henry IV's conversion. Some really interesting details: - Desportes names the exact price that Henry IV accepted to convert to Catholicism: 500,000 écus. - Just two months after these letters were written, Frachetta betrayed Mayenne by handing over Desportes' correspondence to the Spanish ambassador. These letters may explain why he did it: Desportes writes to Frachetta that Mayenne is unable to pay for Frachetta's services allegedly because funds for this payment had to come from a third party (a prelate) and "this is no time to take anything" from these funds. - The letter to Frachetta reads like a piece of detective fiction, with elaborate code words used for names of various parties in Rome involved in an anti-Spanish conspiracy ("our friend at the college", "the man of La Chesne", "our uncle"). You can view the ciphers, their translations to French, and the translation from French to English (with significant historical notes included) at: prinzai.com/desportes-1593/