Castillo de Alcalá la Vieja is a medieval fortress in Alcalá de Henares, Madrid, rising on a clay promontory in the Henares River valley. Built by Muslims in the 9th century under Emir Muhammad I, the castle originally served as "Qal'at'Abd al-Salam," a simple watchtower integrated into the al-Andalus defensive system, before falling to Christian forces in the early 12th century. Today, two defensive towers remain standing after recent restoration, along with ruinous remains of other tower structures and walls, preserving evidence of over a millennium of occupation. The castle's designation as "la Vieja" (the old) reflects its centuries of abandonment after the 13th century, making it a valuable archaeological site documenting the region's Islamic and Christian heritage.
