Castillo de San Martín in Soto del Barco, Asturias, occupies a historically layered landscape built atop Roman fortifications and pre-Roman settlements. The current castle was constructed by Alfonso III over remains of an earlier Roman fortress. The structure features a distinctive square tower with three floors, narrow arrow slits, and 16 crenellations at its crown, surrounded by defensive walls extending toward the Nalón River estuary. The castle adjoins historic structures including the Church of San Martín and 19th-century residential buildings with wooden galleries, creating an ensemble reflecting different centuries of Asturian heritage.
