The Alcázar of Seville is a royal palace in Seville, Spain, built for the Christian king Peter of Castile. It was built by Castilian Christians on the site of an Abbadid Muslim residential fortress destroyed after the Christian conquest of Seville. Although some elements of other civilizations remains. The palace, a preeminent example of Mudéjar architecture in the Iberian Peninsula, is renowned as one of the most beautiful. The upper levels of the Alcázar are still used by the royal family as their official residence in Seville. It is the oldest royal palace still in use in Europe, and was registered in 1987 by UNESCO as a World Heritage Site, along with the adjoining Seville Cathedral and the General Archive of the Indies.