In the last third of the 15th century, in the middle of the conflicts between warring noble families, one of these powerful families, the Almirantes of Castile, built a castle in the historical town of Simancas, close to Valladolid. The Catholic Monarchs, in line with their policy of controlling the nobility, demanded that the Enríquez relinquished the fortress, which is how it was transferred to the crown. It was Carlos V who, on 16 September 1540, following the suppression of the rebel movement, consolidation of royal power and with the monarchy's administrative apparatus in place, ordered that an important set of documents be kept in one of the turrets or towers, which had been made ready for this purpose.
The action of the emperor, however, did not extend beyond gathering together in the newly-created archive a small set of documents that had been scattered around the Kingdom of Castile. The real executor of the Simancas Archive, fully aware of the importance and significance of his archive project, was Felipe II, who clearly saw that the government of an empire must be assured of the control of written documents, the only means by which information was received and orders issued. In order to achieve this objective he had a building constructed and regulations enacted. In 1572 he ordered Juan de Herrera to draw up designs of what was to become the first building in the modern era to be constructed as an archive, and in 1588 he signed an instruction that is considered to be the first ever regulation for archives in the world.
From that moment, the new Simancas Archive began to receive the periodic dispatches of documents from the central bodies of the Spanish monarchy: the Councils during the times of the Austrias (16th and 17th centuries) and the Secretariats in the era of the Bourbons (18th century), though with some exceptions. In 1785 the Council of the Indies was moved to Seville; in the mid-nineteenth century the Council of Aragon was removed to the Archive of the Kingdom of Aragon and, in the first few years of the twentieth century, the Council of the Inquisition was deposited in the National Historical Archive.
The era of the archive at the service of the administration ended in 1844, when, with the arrival of the Liberal Régime, Simancas was opened up to historical research. From that time it became a Historical Archive.
This truly exceptional historical background to the Simancas Archive makes it one of the major archives in terms of studying the modern era.