Castillo de la Raya, also known as the Martín González tower, perches on a hilltop marking the historic border between the medieval kingdoms of Castile and Aragón near Monteagudo de las Vicarias in Soria province. Built between the 12th and 13th centuries by King Alfonso VIII as an advance garrison to monitor the Nágima valley and the crucial Jalón River passage, it remains an important landmark in the region's defensive landscape. Constructed with masonry walls and ashlar stone corners in Gothic and Proto-Gothic styles, the fortress originally contained multiple rooms, a cistern, and underground passages adapted to its dramatic hilltop setting near the hermitage of Nuestra Señora de la Torre. Though currently in progressive ruin, its strategic location between spectacular rocky formations and its role in the Reconquista continue to make it a significant monument to medieval military architecture.