Castle of San Marcos

Castle of San Marcos (also Castillo de Alfonso X El Sabio) is a medieval castle located in El Puerto de Santa María, Cádiz, Spain. The castle was erected as a fortified church by King Alfonso X of Castile. It was built on the site of a mosque of which the wall of the qibla survives. Close to the castle there is a replica of the map of Juan de la Cosa, along with an explanatory plaque; and a little fountain.