creativity. As Christian armies pushedon farther south, Iberia’s remaining Muslim rulers began to fear their days were numbered. When Alfonso the Brave’s enthusiasm carried him a step too far and he prematurely proclaimed himself emperor of all Spain, al-Andalus finally resorted to calling in help from abroad.
It was a fateful mistake.
The Almoravids were a ferocious Muslim sect from the Sahara Desert that had sprung up around a hard-line missionary who insisted on strict discipline and regular bouts of scourging. They had already expanded south to sub-Saharan Africa and north to Morocco, and they were only too ready to hop across the Strait of Gibraltar to Spain. As soon as they arrived, they decided their coreligionists were a bunch of addled sensualists and went home to arm themselves with a fatwa , or legal opinion, confirming their right to depose them. When they returned, the proud Arabs of al-Andalus took a deep breath and caved in. The new caliphate duly reunited the squabbling city-states and beat back the Christians until it, too, grew lax and was chased out of power by the Almohads, yet another all-conquering Berber dynasty that poured over from Ceuta.
The Almohads were even more fanatical fundamentalists than the Almoravids, and they set out to transform al-Andalus into a jihadist state.
Long ago, as Islam had expanded far beyond Arabia, its scholars had divided the world into the dar al-Islam , the House of Islam, and the dar al-Harb , or the House of War. According to that doctrine, the first was duty-bound to press on the second until it withered to nothing. Armed jihad— jihad itself merely means “struggle,” and often refers to an inner striving for grace—was the divinely sanctioned instrument of expansion. As the House of Islam fractured and Muslims fought Muslims, the strong arm of holy war had itself withered away. Yet the Almohads tolerated no such frailty, and besides imposing severe strictures on their fellow Muslims, they declared an everlasting jihad against Spain’s Christians and Jews. In the Almohads’ uprooted and fiercely pruned faith, Christians wereno better than pagans: as worshippers of a divine trinity rather than the one true God, they no longer deserved the status of protected people. The dhimmi who still lived in al-Andalus were given an ultimatum: die or convert. Rather than choose, many fled.
Western Christendom had undergone a similar transformation. Christianity had begun as a humble movement of Jewish sectaries, but when it was adopted as the official religion of the Roman Empire, it had soon made peace with war. Rome’s legions had marched into battle under the cross, and so had successive waves of barbarians, many of whom had themselves been converted to Catholicism at the point of a sword. St. Augustine, the first Christian thinker to frame the concept of a just war, had condemned battles fought for power or wealth as no better than grand larceny, but he acknowledged that violence had to be met with violence in order to keep the peace. The journey from Augustine had wound through marauding barbarians and Vikings, through grand papal dreams and a Europe overshadowed by military camps, until fighting for Christianity was seen as a noble struggle against the Antichrist. To Catholic theologians, as they finally began to unravel the mysteries of Islam, any accommodation between the two faiths made no more doctrinal than practical sense: while Muslims at least acknowledged Christians, however misguided, as their precursors in faith, to Christians the newer religion, intolerably, told them they had got it all wrong.
For all their differences, it was their similarities that most divided the two faiths. Unlike any other major religion, both claimed exclusive possession of God’s final revelation. Unlike most, both were missionary faiths that strove to take their message to nonbelievers, whom they labeled infidels. As universal religions and geographical neighbors, they