The Cross and the Crescent by Richard Fletcher

Forget trivial Crusades, says Felipe Fernández-Armesto: Christianity and Islam coexisted happily for centuries

Civilisations rarely clash. Our myth of a world vulnerable to cultural conflicts is based on the exceptions we remember. Persian and Graeco-Roman antiquity had violent collisions – but, for most of the time, their relations were of mutual tolerance and respect. Korea and Japan have often found it uncomfortable to live next to the Chinese giant; yet it is remarkable how rarely their independence has been threatened by the contiguity. Sedentary and nomadic cultures are often said to be irreconcilably hostile. Yet sedentarists have usually been able peacefully to buy off or assimilate the nomads.

Common notions about the history of Islam and Christendom are disfigured by the prominence our history books give to the occasional flare-ups we call Crusades. This is a trick of the market: war makes rattling good reading, whereas peace is dull stuff.

Most history books depict Islam and Christendom clawing at each other across and around the medieval Mediterranean, like crabs locked in conflict. Nothing could be further from the truth. Relations were almost always peaceful. Mutual persecution did happen, but it was exceptional.

In many places in Spain and the Levant, Christians and Muslims shared veneration for some of the same saints and shrines. At some times and places, their cultures were deeply interpenetrated: some witnesses before the cadi's court in Ummayyad Cordova were so uncertain of the differences between the two communities that they could not say for certain to which they belonged.

Where the communities were "ghetto-ised" in defence of their purity, it was by mutual agreement. Among the many intriguing stories Richard Fletcher tells in his new account of Christianity and Islam from Muhammad to Reformation are those of Ali of Daroca, burned at the stake in 1311 for alleged fornication with a Christian girl who was later found to be a virgin; and of the monks of Roda in 1356, who supposedly got Muslim women enslaved by seducing and then denouncing them. But these were not simple cases of Christian abuse: they were enforcements of laws that Muslims also demanded.

Christian polemicists devised colourful insults for Muhammad – but they were equally uncharitable about each other. Indeed, for most of the period Christians, if they knew anything about Islam, tended to classify it as a Christian heresy, which was not surprising in view of the pious references in the Qu'ran to Christ, his virgin mother and the Abrahamic tradition.

As well as common origins in Jewish religion, Islam and Christendom shared a background in Graeco-Roman civilisation. Mehmet the Conqueror, as Fletcher reminds us, identified with Alexander the Great; Filelfo flattered the Turks by likening them to the Trojans – recovering Agamemnon's ill-gotten gains. Most of the science salvaged from the wreck of classical antiquity was preserved in Muslim hands and retrieved by the west at Muslim courtesy.

The Crusades were religious wars in a sense: at least on the Christian side, participation was an act of penance for the recovery of "holy" lands, where divine or saintly feet had trod and where soil was hallowed by relics. Usually, however, the motives were political and economic. Mercenaries and allies crossed credal lines. The supposed hero of the Crusades in Spain, El Cid, spent most of his career as a freelance fighting for Muslim rulers. Some of Fletcher's best stories are of the permeability of frontiers between Islam and Christendom, by lovers, traders, artists, physicians and flatterers, as well as by soldiers and politicians.

He shows that what really vitiated relations between Islam and Christendom was not ingrained hatred or cultural aversion, but ignorance on the Christian side and indifference on the Muslim. Because Muhammad's revelations had supplanted those of earlier prophets, Muslim scholars turned to the doctrines of Jesus very rarely, and only in order to refute them. Crusading propaganda, of which the Chanson de Roland is Fletcher's preferred example, whipped up hatred – but not of Islam, only of a fantasy-simulacrum which bore no relationship to the real thing. The enemies depicted in the Chanson are not Muslims but pagans, who worshipped three idols "in a sort of parody of the Christian Trinity".

On the Muslim side, the indifference remained. Christendom was a manifestly inferior civilisation with little to teach richer, more advanced neighbours. The Crusades were "pinpricks" almost unworthy of record. In the long run, Fletcher argues, this complacency proved fatal to Muslim superiority. The hare ignored the tortoise and lost the race.

Christianity took over as the world's most successful religion as Islam's "cultural adaptability ran out". Christians, however, always had good reason to study Islam and eventually began to understand it. In Fletcher's chronology, "the first steps" were taken in the 13th century, when Western scholars began to see Islam as a distinct culture rather than "an aberrant form of Christianity". By the mid-15th century, John of Segovia and Nicholas of Cusa embraced a real vision of pluralism – what we would call a multi-civilisational world – in which the cause of religious convergence would be advanced peacefully by dialogue and persuasion.

Of course, that was not how things worked out, because of the ineradicable importance of what Fletcher calls "a geology of human relationships which it is unwise to neglect". We do have a chance now, however, if we re-excavate that archaeology and get our history right, to build a peaceful, multi-civilisational future. But just as belligerent princes wrecked the eirenic vision of 15th-century scholars, so ignorant politicians seem hell-bent today on war. They should read Fletcher's book.

Not everything in it is unchallengeable: his claim, for instance, that Christian disunity is doctrinal whereas divisions in Islam are about authority, or his insistence that the Ottomans lacked interest in Western science, or his dodgy etymology of the word "bible". But it is an important book for our times, as well as a feat of compression, and a triumph of good sense.

Felipe Fernández-Armesto's 'Food: a history' is published by Pan