The collapse of empires in the central and eastern Mediterranean was matched in the far west by the disintegration of Almohad power. The caliphs lost their enthusiasm for the extremist doctrines of Almohadism, and were accused of betraying the principles of their movement. Following military defeat at the hands of Christian kings of Spain at Las Navas de Tolosa in 1212 the caliph is said to have been strangled by one of his slaves. The Almohad territories in Spain and Tunisia fell into the hands of a new generation of local kings who only paid lip-service to Almohadism. The Hafsid rulers who gained control of Tunis proclaimed themselves successors to the Almohad caliphate, though more as a way of asserting their legitimacy than out of deep commitment to Almohad beliefs. The Berber Marinids broke Almohad power in Morocco in the mid-thirteenth century, after a long struggle. At the same time the Nasrid dynasty established itself in Granada, where it would last until 1492; it adhered strictly to Sunni Islam, not Almohadism. The thirteenth century also saw a major transformation in the Christian western Mediterranean: Pisa’s rivalry with Genoa for mastery over the waters around Corsica and Sardinia culminated in Pisan defeat at the battle of Meloria and the loss of iron-rich Elba in 1284. Although the Pisans did not yet lose control of the large areas of Sardinia they ruled, and even recovered Elba, a new rival to both Pisa and Genoa emerged, not a maritime republic but a group of cities led by Barcelona and backed by the growing power of the king of Aragon and count of Catalonia, James I ‘the Conqueror’. The Mediterranean vocation of the kings of Aragon was not obvious before the thirteenth century. Lords of a small, mountainous kingdom that only toppled the Muslim emirate of Saragossa in 1118, they dissipated much of their energy in attempts to interfere in Christian Castile and Navarre. But in 1134 King Alfonso ‘the Battler’ of Aragon died, having failed to produce an heir; his brother, a monk, was forced out of his convent in order to breed.