The Duero river valley was contested ground for centuries. Muslim and Christian forces traded control of the Gormaz site repeatedly -- chronicles record Muslim reconquests in 925 and 940, evidence that the location was already fortified before the castle that stands today. The current structure was built or rebuilt in 965-966 by Ghalib ibn Abd al-Rahman, a general serving the Caliph al-Hakam II of Cordoba. A foundation stone bearing the caliph's name and the construction date was found at the nearby Hermitage of San Miguel de Gormaz and is now kept at the Burgo de Osma Cathedral. The castle anchored a network of watchtowers stretching in every direction -- some dating to the mid-eighth century -- that formed an early warning system along the volatile frontier between Islam and Christendom.

The castle changed hands multiple times through the tenth and eleventh centuries, sometimes through siege, sometimes through political negotiation. In 975, General Ghalib relieved the fortress and pursued Christian forces into Castile. By 983, the Muslims had recaptured it again. During the political chaos of the Fitna -- the civil war that fractured the Caliphate of Cordoba -- the caliphs reportedly promised Gormaz to Sancho III of Navarre in 1009 or 1011, though whether the handover occurred is unclear. Fernando I of Leon captured the fortress in 1059. Archaeological evidence suggests Muslims were still maintaining the castle into the 1060s, but by century's end, the entire Duero region had come under definitive Castilian control. In 1087, Alfonso VI gave the castle to Rodrigo Diaz de Vivar -- El Cid -- Spain's most legendary warrior, cementing Gormaz's place in both history and myth.

The castle's main gate is a masterwork of Caliphal design. Two monumental horseshoe archways stand one behind the other, creating a narrow killing zone where defenders could rain projectiles on attackers from above. The outer archway, 2.76 meters wide and 7 meters tall, was once framed by an alfiz -- the rectangular decorative border characteristic of Islamic architecture -- covered in stucco and possibly painted with false voussoirs and Arabic inscriptions. The decorative style links Gormaz directly to the Great Mosque of Cordoba and the palace city of Madinat al-Zahra, the twin jewels of the Caliphate. Inside, the castle divides into two distinct zones: an eastern citadel with higher, heavier walls serving as a keep and last line of defense, and a larger western section spacious enough to house an entire army. Archaeologists have identified what may be the remains of a musalla -- an open-air prayer space -- marked by a white mortar floor. Both zones had their own cisterns, ensuring water during siege.

The castle saw its last significant military use during the fourteenth century, when it became a strategic prize in the conflict between Pedro I of Castile and Pedro IV of Aragon. During this period, a small urban settlement grew within the castle walls, and extensive repairs were carried out. Afterward, Gormaz was abandoned and slowly crumbled. Modern excavations began in 1922 and accelerated in the late twentieth century under archaeologist Juan Zozaya. Today, the northern wall -- built of large rough stone with fifteen towers spaced at regular intervals -- remains remarkably intact, while the southern wall, constructed with more sophisticated carved-stone masonry, has suffered more severely from erosion and landslides. Walking the kilometer-long perimeter, you cross a landscape that is one of the oldest standing ensembles of military architecture in Western Europe -- a place where two civilizations built, fought, and left their marks in stone.