The ‘Romans’ of Justinian’s day knew they were very different from other men and were proud of it. They belonged to a particular civilization; some of them, at least, thought it was the best conceivable. They were not unique in this. The same was true of men in other parts of the globe - in, for instance, China. Long before the birth of Christ, civilization had been at work in every continent except Australasia, deepening and quickening the divisions opened in human behaviour in prehistoric times. Mankind’s cultural variety even in the earliest historical times was already escaping any but the finest net, and when the classical Mediterranean world had at last cracked apart irreparably - ad 500 will do as a rough marker - the world was full of contrasting cultures.
Most of the globe’s surface was then still without civilization, but what was civilized fell into relatively few zones in each of which powerful, distinctive, often self-conscious and largely independent traditions were at work. Their differences were to go on deepening for another thousand years or so, until by about 1500 mankind was probably more diversified than ever before or since. There was still no single dominant cultural tradition.
One result was that Chinese, Indian, western European and Islamic civilizations all lived independently long enough to leave ineradicable traces in the ground-plan of our world. They coexisted and part of the explanation, paradoxically, is that in one respect all these civilizations were much alike. Broadly speaking, they were all based on subsistence agriculture and all had to find their main sources of energy in wind, running water, and animal or human muscles. None of them could bring to bear overwhelming power to change the others. Everywhere, too, the weight of tradition was enormous; the unquestioned, if different, routines under which all mankind then lived would seem intolerable today. Of course, variety in cultural development had already produced different technologies. It was to be a long time before Europeans could again undertake engineering on the Roman scale, yet the Chinese had long before that discovered how to print with movable characters and knew about gunpowder. Nevertheless, the impact of such advantages
or disadvantages was only marginal, largely because intercourse between traditions was difficult except in a few favoured areas. Yet the insulation of one civilization from another was never absolute; there was always some physical and mental interaction going on. The barriers between them resembled permeable membranes rather than impenetrable walls, though for the most part men in these times lived contentedly in traditional patterns, ignoring others following other ways a few hundred - or even a few score - miles from them.
This great era of cultural diversity spans a very long time. In some traditions we must go back to the third century BC to resume the story, and the breaches in the defences which separated them from others only became irreparable well after 1500. Before then, most civilizations moved largely to rhythms of their own, only occasionally showing the effect of major disturbance from outside. One such disturbance, which affected men from Spain to Indonesia, and from the river Niger to China, originated in the Near East, the zone of the oldest civilized traditions and the logical place to begin to examine this diverse world.