The king was Ferdinand of Aragon; and he and his wife, Isabella of Castille, financed the expedition that sent Christopher Columbus west with the intention of going east, resulting in his landing in the Caribbean and launching a drive toward colonization of the Americas.

King Ferdinand used a secret code to issue instructions to his top military commander, Gonzalo de Córdoba, during their country's campaigns in Italy in the early 1500s. Spain and France were fighting for control of the Kingdom of Naples; Spain ultimately claimed rule of the kingdom in 1504, by which time Columbus had completed his fourth and final voyage to the New World.

The code contained 88 different symbols and 237 combined letters. Each letter of the normal alphabet was represented by between two and six figures, such as geometric shapes. Among the finds in the instructions from King Ferdinand to Córdoba were ordinary instructions like battle commands but also an admonishment for the commander's not consulting the king before launching diplomatic efforts.

The letters are now on display at the Army Museum in Toledo. In conjunction with the exhibition, the museum sent two letters written between 1502 and 1506 to members of the Spanish intelligence agency. At the bottom of one of the letters were some sentences out of code; still, it took the codebreakers six months to crack the code.