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The recent heightening of tensions between the Islamic world and the West, particularly since the events of 9/11, has prompted a number of scholars to reassess that often-troubled relationship. The latest to enter the fray is David Levering Lewis, better known for a series of influential works on modern history, notably his prizewinning study of the black civil rights activist W. E. B. Du Bois.

In God's Crucible, Lewis provides a stirring, albeit occasionally disjointed, account of the rise of Islam in the early 7th century, its spectacular military successes at the expense of the war-weary Byzantine and Persian empires, and above all its complex, intellectually fertile yet simultaneously fractious relationship with Christian Europe down to the early 13th century.

Lewis takes as the central theme of his work what he calls the "clash of civilizations" between the Islamic Caliphate and the Frankish Empire. The problem with this approach is that Muslim-Frankish conflict, which first flared up in the 8th century, diminished markedly as the 9th century wore on. The subsequent decline of Islamic civilisation in the Iberian Peninsula, where its imprint was most firmly felt, was due in far greater measure to the military expansionism of the Christian states of the north.

Yet Lewis devotes relatively little attention to these Christian societies and offers only the sketchiest of accounts of their origins and expansion. Thus, while the legendary Frankish warrior hero Roland gets ample billing, an emblematic figure such as El Cid is consigned to only the briefest of walk-on roles.

Lewis's portrait of the Christian world, north and south of the Pyrenees, is unremittingly bleak. Whereas Muslim Iberia is depicted in glowing terms as a society "secure in its defences, religiously tolerant, and maturing in cultural and scientific sophistication", the Christian territories are variously categorised as "religiously intolerant", "fanatical", "intellectually impoverished", "fratricidal" and "sectarian". The Frankish economy is dismissed as being "little better than late Neolithic".

This overwhelmingly negative, two-dimensional view of the Christian world could and should have been substantially qualified or nuanced at every turn, not least with regard to the relative degrees of religious tolerance that existed on either side of the ideological frontier, a subject that has been much debated in recent scholarship. By not doing so, Lewis's account is left looking seriously lopsided.

There are other concerns too. For one thing, Lewis rarely pauses to consider the difficulties that his sources present. Anecdotal or legendary episodes, many of them penned long after the supposed event - such as the appearance of St James to Ramiro I of Le¨®n at the battle of Clavijo in 844 - are often presented as bald fact. There are also a number of factual errors of varying degrees of seriousness. Thus, the suggestion that the Barbastro campaign of 1064 was in some way a proto-Crusade has now been discredited; and it was not Sancho II of Castile who was reputedly pushed off a cliff to his death, but his namesake and contemporary Sancho IV of Navarre who held that dubious honour.

Furthermore, Lewis occasionally indulges in comparisons with modern history that are neither helpful nor exact. Thus, the Sassanian campaigns in Asia Minor of the early 7th century are compared to the Nazi Blitzkrieg; the caliph 'Umar's triumphal entry into Jerusalem in 638 is paralleled with Hitler's arrival in Paris in 1940; the Venerable Bede is dubbed "the Einstein of the Middle Ages"; and the Franks are likened to the cowboys of the 19th-century American West.

Lewis deals with the broad sweep of history with commendable enthusiasm and his book will doubtless be read with enjoyment by those who like their history painted in bright colours and do not wish doubts and complexities to get in the way of a good story. But the book's publicists' bold claim that it "will redefine what we thought we knew about the history of Islam and provide new understanding of the modern world" proves sadly wide of the mark.