Sea of Faith: Islam and Christianity in the medieval Mediterranean world by Stephen O'Shea

A glittering insight into hostile faiths

This seemingly cosmetic shift of perspective has vast ramifications: you stop thinking of Muslim and Christian states, even of spheres of influence, since these shift all over the place. Every page carries a glittering freight of insight, detail and sometimes caustic observation. The breadth of research is intimidating, but the author tells his story with an engaging blend of swagger and sensitivity. You are caught up by this vast wave of learning, but never cast down.

O'Shea has walked the walk, quite literally. He has visited the battlefields on foot, and relays to the reader the very different fashions in which they have been commemorated. Poitiers (732), where the shield wall of Charles Martel's troops refused to collapse before the Arab onrush, has a great chess board graven into the ground; Manzikert has a beautiful, desolate 11th-century graveyard, a place of pilgrimage; Yarmuk needs no memorial; the Golan Heights above it say it all.

But why these battles in particular? Why not a host of other encounters? For this framework often simply allows an eager author to run through his favourite encounters. An opportunity for the bold scholar can also be an excuse for the lazy dilettante. Happily though, O'Shea justifies his selection with shrewdness and panache. Only the fall of Cordoba fits uncomfortably into this frame. While I understand that the fall of the Umayyad caliphate represented the end of a golden era of "convivencia", it was not, strictly, brought about by a clash with Christianity.

But while this is ostensibly the story of a long war, its main interest lies in the sporadic fits of peace recorded. In Muslim Spain and early Christian Spain, Muslim Sicily and early Christian Sicily, Muslim Palestine and early Crusader Palestine, deep and beautiful accords were established. But "early" should make the point. For while The Sea of Faith is not a story of unremitting hostility, it shows, sometimes inadvertently, that the cuckoo shares his nest no more readily than the leopard changes his spots. Whatever the merits of convivencia, the beautiful ideal of all the peoples of the book living together in respectful harmony, its terms were dictated by the stronger party.

The tale of Moslem and Christian relations has as its master theme nature abhorring vacuums and moving into them. The Byzantine defeat at Yarmuk (636) showed the essential hollowness of a state which thought that its citizens could be neglected, even oppressed, as long as the army could protect the frontiers; but after Yarmuk, the persecuted, embittered and pauperised inhabitants of Syria welcomed the invaders with a groan of relief.

In his rightly celebrated book, The Perfect Heresy, the story of the Cathar community of Southern France and of its destruction, O'Shea occasionally fell prey to convulsions of grating jargon. There's not much of that here, but his prose is often over-confident. Clauses like "the harshness of conquest could not be washed away in rose water" (who would ever suppose it could?) tell us that he needs to calm down. He says "western" when he means west. And his love of the vivid verb propels him into irresponsible errors: the Greeks did not "spurn" the talents of a cannon-maker when it became clear that Constantinople was to be attacked: they simply couldn't afford his fee.

It is in the unravelling of happenstance that O'Shea shows his brilliance: coincidences, patterns, lines of beauty - or of ugliness. The battle of Manzikert (1071), for example, not only opened the way for the Turkish invasion of Byzantine Asia Minor but set the seal on the division of Shia and Sunni, and at almost the same time as a bigoted cardinal of the Roman church anathematised a bigoted Patriarch of the Orthodox.

O'Shea's hatred of divisiveness sometimes drags him into eccentric positions. To the second greatest foe of the Monothelite compromise, Patriarch Sophronius of Jerusalem, he ascribes "satisfaction at dashing Christian unity", which isn't just uncharitable, it's unimaginative: even the most cursory acquaintance with the religious mindset teaches that sometimes defence of the truth (however you perceive it) is more important than unity. The greatest foe of Monothelitism, Maximus the Confessor, is not mentioned at all, perhaps because his well-attested sanctity proved inconvenient for O'Shea's vision of nasty old clerics scuppering the spirit of civilised give-and-take.

The tentative optimism with which the book concludes is unsettlingly glib. O'Shea invokes Spain and Turkey as "nowadays the most culturally expansive [countries] in outlook toward the worlds still labelled, by some, Christian and Muslim". I wish he had elaborated. Spain, perhaps, but Turkey? The two central images of the book remain the Mezquita in Spain, once a mosque, now a cathedral, and Agia Sophia in Turkey, once a church, then a mosque, now a museum. Convivencia was in many ways a more settled system than our modern multiculturalism, but it was always delicate, the product of briefly ideal conditions. I wonder whether the two buildings he invokes as images of hope really serve his turn. However you look at it, the beautiful, improbable Mezquita is still a raped building; grand, grey, Agia Sophia a neutered one.