The Moorish power reached its height in the tenth century, and gradually declined in the eleventh, when it broke up into petty and short-lived kingdoms. The Almoravides from Africa began their rule in Spain about 1090. This dynasty was overthrown by the Almohades in 1145, and the latter became extinct in Spain in 1257. After the disruption of the realm of the Almohades, the Moorish kingdom of Granada was established, and was held in vassalage to Castile, of which Ferdinand and Isabella, in 1474, became joint sovereigns. The Moors made Granada, their capital, a large and powerful city, and there in the thirteenth century they built their magnificent palace and citadel, the Alhambra, the finest example of Moorish architecture and decorative art. In 1482, having prepared themselves for what proved a final struggle with the Moors, Ferdinand and Isabella began the war against Boabdil, the King of Granada, who the year before had seized the throne from his father, Muley Hasan. After some early reverses and later interruptions--during which the wavering Ferdinand was held to his purpose by the rebukes and encouragement of his stout-hearted Queen--the Christian sovereigns reduced the strongholds of the Moors, until by 1490 the more important half of the kingdom of Granada had been conquered. The city and its small surrounding district alone remained to Boabdil. On April 23, 1491, Ferdinand and Isabella encamped before Granada with fifty thousand foot soldiers and ten thousand horse, and the last contest began. Though Granada was shorn of its glories, and nearly cut off from all external aid, still its mighty castles and massive bulwarks seemed to set all attacks at defiance. Being the last retreat of Moorish power, it had assembled within its walls the remnants of the armies that had contended, step by step, with the invaders, in their gradual conquest of the land. All that remained of high-born and high-bred chivalry was here; all that was loyal and patriotic was roused to activity by the common danger; and Granada, that had so long been lulled into inaction by vain hopes of security, now assumed a formidable aspect in the hour of its despair.