The fortress that we see today was mostly erected in 1328 by King Alfonso XI of Castile, but takes its name from Isabella of Castile and Ferdinand of Aragon, who stayed here several times during the second half of the 15th century, preparing the campaign against the Muslim Caliphate of Granada. Alfonso's castle retained only part of the Moorish fortress, but the structure still appears Islamic because the king employed Moors craftsmen who were living in town after the Christian conquest. The Kings of Castile also maintained the gardens; indeed a set of orchards have existed in this area since at least the 10th century, when Caliph Abd al-Rahman III constructed an aqueduct to bring water from the waterwheels of the river. The building also houses an important collection of mosaics and Roman remains that remind us that the site was also the home of Roman governors.