The Castle of the Counts of Modica is Alcamo's main landmark, a squat four-towered fortress in the middle of town. It was probably begun in the 14th or 15th century and later became the residence of the Counts of Modica, one of the great feudal powers in western Sicily.
Its later life was less grand: the castle served as a prison until the 20th century. The heavy walls and compact plan still make it the clearest reminder that Alcamo was once a fortified inland town, not just a service centre for the coast.