Despite a resurgence during the 10th century, the Caliphate of Córdoba's attempts to reverse the Reconquista failed, and by the 11th century, Christian Iberia was united under Sancho the Great, the King of Navarre, whilst the caliphate was divided and engulfed by civil war, the period of the "taifas". The 11th century saw the development of a concept of Christian holy war, to be waged against Islam with the purpose of the Christians recapturing long lost territories – the Crusade. Crusading, under other names, also took place in Spain; Franks and Normans and even Papal troops took to Spain in increasing numbers to join the locals in their fight against "the Moor." The last threat of the 11th century came in the form of the Almoravids, who with their well disciplined forces first established a hegemony over Morocco and then extended it over al-Andalus. While the "Reconquista" paused in the west, to the east Alfonso the Battler, the King of Aragon, redoubled efforts to retake the valley of the Ebro. In 1212, the "Reconquistadores" gained a decisive victory over the Almohads at the Battle of Las Navas de Tolosa. Shortly after the battle, the Castilians took Baeza and, then, Úbeda, major fortified cities near the battlefield, and gateways to invade Andalucia. Thereafter, Ferdinand III of Castile retook Córdoba in 1236, Jaén in 1246, and Seville in 1248; then he took Arcos, Medina-Sidonia, Jerez and Cádiz, effectively bringing the bulk of the reconquista to a conclusion.