This fortress was built at the end of the Middle Ages between 1468 and 1492, by the II Duke of Medina Sidonia, Don Enrique Perez de Guzmán y Fonseca, The Magnificent, natural son of Don Juan Alonso Perez de Guzmán I Duke of Medina Sidonia and Isabel de Fonseca y Ulloa.
Evidence of its construction lies in the symbols carved in stone, called SEGUR, a type of butcher's hatchet. In the Middle Ages, it was common for nobles to bear other symbols specific to their family, in addition to the heraldic symbols they inherited, as is evident in the Mermaid Gate and the vault of the Aula Maior.
For some time it was called the New Alcázar, because prior to its construction there was another Alcázar located some distance to the east of the Castle.