The (Old) Castle of Alcoutim is a medieval castle built onto a prehistoric castro located in the civil parish of Alcoutim, municipality of the same name, in the Portuguese Algarve. About one kilometre (0.62 mi) north of the town of Alcoutim, the old castle is one of the more important Islamic military structures in the Algarve: it is both an important historical visit for tourists and historiographically significant to the Muslim occupation of the region. Commonly confused with the younger Castle of Alcoutim, the old castle was abandoned in the 11th century, but its exploration and excavation was elaborated by archaeologists in the 20th century.