Religious tradition has defined human societies and shaped their habits of mind more strongly than any other factor. It still does, even in communities which have lost their collective belief in God. Indifference to formal creeds may be common to the governing elites of most countries, and in Europe to their electorates as well. Yet the world is still living with the consequences of centuries of mutual hostility and incomprehension among the three great monotheistic religions of the Mediterranean.
The sudden birth of Islam and its rapid and violent spread through North Africa and the Middle East in the seventh century shattered the political and intellectual certainties of Europe more completely than the Germanic invaders of the Roman empire had ever done. The 'barbarians' from the north had been drawn by the wealth and prestige of the empire, and were absorbed, civilised, Christianised by their victims within a few generations of their arrival. The Islamic conquests were quite different. Here were conquerors with certainties of their own. The only civilisations which they absorbed were those, like the Persian, which they converted to Islam. The unity of the Mediterranean world, which had been the dominant geographical fact of the ancient world, was broken for 12 centuries until the colonial empires re-established it on European terms in the age of Napoleon and Kitchener. For most of the intervening ages, an iron curtain divided the self-contained world of Islam from Christian societies.
The chinks and gaps in the curtain are the subject of Richard Fletcher's interesting extended essay on cross and crescent in the Middle Ages. Much of his material is familiar, but he has a graceful way with words and ideas, and brings plenty of ideas of his own to his vast theme. He deals with the Arab transmission of Greek science and philosophy, with their role as commercial intermediaries between Europe and the east, with the products which Europe took from the Islamic world: cotton, cork, calculating machines. He has a lot to say about the frontier zones where Christians and Moslems came into direct contact, in Palestine, Sicily and Spain. The first two were perhaps too short-lived to matter, except as a source of exotic anecdotes. But Spain is another matter: a truly porous frontier region, where Christian and Moslem communities lived in close proximity for most of the Middle Ages. Spain's rejection of its Islamic (and Jewish) past in the 16th century is one of Europe's cultural tragedies.
One can already detect, at the end of Fletcher's period, some of the factors which were eventually to transform the powerful and self-sufficient Islamic world of the eighth and ninth centuries into the resentful and dependent client of the West which it became by the 19th. Gunpowder, which reached Europe in the 14th century, was probably the last major technology to be imported by Europe from the east, but already by the 16th century the Turkish sultan's principal gun-makers were Germans. Intellectually self-contained systems of belief stagnate. One of the most striking features of the Islamic world through the Middle Ages is that, in spite of its comparative tolerance for other 'people of the Book', it showed almost no curiosity about them. This may have been understandable in the time of Charlemagne. But in the late Middle Ages the great Arab travellers and geographers still had very little to say about Christian Europe, and that inaccurate. Yet European travellers were already beginning to explore central Asia and China, and Italian and Portuguese seamen were discovering the sea route to the east which would shortly turn Islam's flank. In this failure of curiosity lay the origins of Islam's technical and military inferiority in later centuries, and the experience of colonial rule and European migration which has poisoned relations between Islam and the West in modern times.