Measured in years, more than half the story of civilization is over by about 500 BC. We are still nearer to that date than were the men who lived then to their first civilized predecessors. In the three thousand or so years between them, humanity had come a long way; however imperceptibly slow the changes of daily life in them had been, there is an enormous qualitative gap between Sumer and Achaemenid Persia. By the sixth century, a great period of foundation and acceleration was already over. From the western Mediterranean to the coasts of China a variety of cultural traditions had established themselves. Distinct civilizations had taken root in them, some firmly and deeply enough to survive into our own era. Some of them lasted, moreover, with little but superficial and temporary change for hundreds or even thousands of years. Virtually isolated, they contributed little to mankind’s shared life outside their own areas. For the most part, even the greatest centres of civilization were indifferent to what lay outside their spheres for at least two thousand years after the fall of Babylon, except when troubled by an occasional invasion. Only one of the civilizations already discernible by the sixth century BC in fact showed much potential for expanding beyond its cradle - that of the eastern Mediterranean. It was the youngest of them but was to be very successful, lasting for over a thousand years without a break in its tradition. Even this is less remarkable than what it left behind, though, for it was the seedbed of almost all that played a dynamic part in shaping the world we still inhabit.