East by its successor state, the Byzantine Empire. Byzantine architecture is an example of such cultural diffusion continuing even after the collapse of the empire. Nevertheless, the Guadalquivir River valley became the point of power projection in the peninsula with the Caliphate of Córdoba making Córdoba its capital. The Umayyad Caliphate produced such leaders as Caliph Abd-ar-Rahman III (ruled 912–961) and his son, Caliph Al-Hakam II (ruled 961–976) and built the magnificent Great Mosque of Córdoba . Under these rulers, Córdoba was the center of economic and cultural significance. By the 10th century, the northern Kingdoms of Spain and other European Crowns had begun what would eventually become the Reconquista: the reconquest of the Iberian Peninsula for Christendom. Caliph Abd-ar-Rahman suffered some minor military defeats, but often managed to manipulate the Gothic northern kingdoms to act against each other's interests. Al-Hakam achieved military successes, but at the expense of uniting the north against him. In the 10th century the Saracen rulers of Andalusia had a Slavic army of 13,750 men. After the conquest of Toledo in 1086 by Alfonso VI, the Crown of Castille and the Crown of Aragon dominated large parts of the peninsula. The main Taifas therefore had to resort to assistance from various other powers across the Mediterranean. A number of different Muslim dynasties of North African origin—notably Almoravid dynasty and Almohad dynasty—dominated a slowly diminishing Al-Andalus over the next several centuries. After the victory at the Battle of Sagrajas (1086) put a temporary stop to Castilian expansion, the Almoravid dynasty reunified Al-Andalus with its capital in Córdoba , ruling until the mid-12th century. The various Taifa kingdoms were assimilated. the Almohad dynasty expansion in North Africa weakened Al-Andalus, and in 1170 the Almohads transferred their capital from Marrakesh to Seville. The victory at the Battle of Las Navas de Tolosa (1212) marked the beginning of the end of the Almohad dynasty. Crown of Castile The weakness caused by the collapse of Almohad power and the subsequent creation of new Taifas, each with its own ruler, led to the rapid Castile reconquest of the valley of the Guadalquivir. Córdoba was regained in 1236 and Seville in 1248. The fall of Granada on 2 January 1492 put an end to the Nasrid rule; an event that marks the beginning of Andalusia, the southern four territories of the Crown of Castile in the Iberian Peninsula. Seven months later, on