For over 500 years, four letters between King Ferdinand of Aragon and one of his commanders, Gonzalo Fernandez de Córdoba, have puzzled historians. They used a completely unique code with more than 200 different characters to communicate and nobody had been able to crack it – until now.

The Spanish intelligence agency, CNI, has finally been able to solve the code and reveal the contents of the correspondence between the two high-powered men. The letters date from the time of the Naples War in the first few years of the 1500s, when King Louis XII of France was fighting against Ferdinand and Isabella of Spain for dominion over southern Italy.

"In the historical situation of that time, in the Naples war, which affected mainly France and Spain, but also the Germanic Empire, the Papal States, the Ottoman Empire and the Italian State Cities, it was essential to keep the secrecy in the negotiations in military strategies and even in betrayals, and any neglect at one point could disrupt strategies," Jesús Ansón Soro, the technical secretary of the Museum of the Army of Toledo, where the letters are on loan, said in a press conference.

Córdoba, also known as the Great Captain, led Spain's military expedition so the commander and the king had to communicate frequently. The four encrypted pieces of mail helped historians understand the context of several other letters that have been found. Among the coded ones, there’s an extra special one hand-written by the king himself, an extremely rare finding since the monarch would have had people writing letters for him usually.

Cracking the code took six months (not least because some of the letters are 20 pages long). They discovered 88 different symbols and 237 combined letters. Some of the symbols corresponded to specific letters, but sometimes it changed or corresponded to a whole word. Sometimes the symbols were even red herrings. They were written without spaces or punctuation making the translation even harder. Deciphering the code was possible though thanks to a decrypted part in one of the letters, which became a key for the researchers.   

The four letters focus on both military and civil matters, discussing a variety of issues. Sending troops, collecting taxes, and administering justice were top priorities in the war but there were also discussions of marrying Spanish officers to southern Italian widows to favor greater social integration. The letters also show that Córdoba was loyal and obedient to the king.

[H/T: Radio Television Española]