This is sweeping, broad brush history; it is also truncated and flawed. Awash with bold narrative and graphic detail, it cuts through large chunks of time, from the late sixth century to the beginning of the thirteenth. The central thesis is announced in the subtitle. Islam, asserts Lewis, was not just a critical force but the defining element in the emergence of what later became Europe. This is not a novel thesis. It has been told and retold, asserted and contested, by numerous historians: Henri Pirenne in the 1930s evoked the hostile frontier, while Americo Castro in the late 1940s offered the amicable synthesis. Pirenne saw the Arab conquests as the death blow to the mare nostrum of Roman/Byzantine civilization, replacing it with two hostile civilizations that faced each other across the sea. Castro, by contrast, imagined Islam as a goad to convivencia, or living together, the possibility that two, or three, variant religious traditions could find and share a cosmopolitan center, one located on European soil, in al-Andalus. Lewis, citing Pirenne, challenges his thesis but then, oddly, goes on to confirm it.

And what was the promise of European revival? We are not told.

It is beyond dispute that Muslim conquests, followed by nearly 800 years of Muslim rule, did change the face of southern Europe. Instead of a collective cultural efflorescence, however, Lewis depicts a catena of historical and cultural exchanges that occasionally produced symbiosis between Arabs and Jews (p. 355), but never between Christians and Muslims. Especially in the period that follows the rise of the Fatimid dynasty in North Africa and Egypt (tenth century on), Islam is increasingly depicted in negative terms as fundamentalist, literalist, fanatic (pp. 320, 356, 358, 360). The final chapter highlights the rejection of rationalism, by both Muslims and Jews. Two notable exceptions were also contemporaries: Ibn Rushd (Averroes) and Musa ibn Maymun (Maimonides).

The book is uneven in structure: Chapters 1–4 portray Islam before intercalating Islam with Christianity in Chapters 5–8. There follows the emergence of Carolingian Christianity (chs. 9–11), before a chapter each on Islam and Christianity (chs. 12–13), which are followed by yet another intercalation of Islam with Christianity (chs. 14–15). One wonders where and how the final message will be delivered in Chapter 16. Alas, the suspense is not justified, for instead of a nuanced perception of multiple, competing forces and uncertain outcomes, Lewis devotes the final chapter of a quite long book to a mere thumbnail depiction (less than twelve pages) of the shadow of philosophical wisdom cast by Averroes and Maimonides. Their rejection by co-religionists prefigures the blood and gore of battle, in this case, the 1212 Battle of Las Navas de Tolosa, which then sets the stage for a papal decree institutionalizing difference, religiously defined and culturally projected, as “unassimilable “otherness” (p. 372).

It seems that the European revival, inaugurated by the eighth-century coming of Islam, produced a thirteenth-century Europe forever defined by the incommensurability, the unassimilable otherness, of the two dominant cultures of the Mediterranean Sea. What is most unsettling about this conclusion is not just its abruptness but its seamless invocation of the Crusades and Crusading Popes, as though papal obiter dicta define all Christians and all Muslims, while also disposing of all Jews, for time immemorial. Left out of the story is the rest of European history that shaped the Crusades and also evokes something less than a siren salute to Christian unity. In 1095, when he preached the sermon in Clermont that was later identified as launching the Crusades, Pope Urban II was trying to reassert his own, and Rome's, leadership over a divided Christendom. The split with the East had been formalized in 1054 (a date left out of Lewis's Chronology, xi–xv), and it was only when the Byzantine Pope feared attack by the Turkish Seljuks that he appealed to Urban for help, providing the Roman Pope with a pretext to call for armed pilgrimage to recapture Jerusalem but also to reunite Christendom.

Lewis's account of “European revival” omits the unintended consequences of the Crusader movement. Urban II began a movement different than he had either imagined or hoped for. It did find an appeal, but chiefly among elements marginal to the early twelfth-century Mediterranean world. Once mobilized, they pursued policies and took actions, often brutal and murderous, that were neither anticipated nor condoned by the Pope. Only later generations, looking for European roots, romanticized these vagabond adventurers as daring agents of faith. Moreover, it was only under Innocent III, with whom Lewis ends his account, that there emerged a full blown ideology of crusading. It, not events in Spain, made religious labels — Muslim and Christian — the badge of honor/dishonor for Crusaders. Even the term “Crusaders” was a later development, inaugurated by Clement III (1187–91), who instructed canonists to describe the Christian volunteers not as peregrine or pilgrims, as they had been designated in the first two Crusades, but rather as cruce signati, those marked by the sign of the Cross, or Crusaders. To invoke the Crusades without suggesting their complex history has the effect of validating this jingoistic shibboleth of politically-motivated religious warfare. It seems to confirm as inevitable and insurmountable a civilizational divide between North and South, Christian and non-Christian, but especially Muslim. While Lewis's prose is lapidary, its message is lethal: Islam and Muslim culture are forever separated from Spain and Christian, i.e., Catholic, culture.