learned the lesson taught by the successful retreat of the ten
thousand, and, just before his death, was preparing to attack the
Great King (of Persia) with all the forces which his supremacy in
Greece put at his disposal. His son Alexander the Great carried
out Philip's intentions. Within twelve years (334-323 B.C.) he had
conquered Persia, Parthia, India (in the strict sense, _i.e._ the
valley of the Indus), and Egypt. After his death his huge empire
was divided up among his generals, but, except in the extreme east,
the whole of it was administered on Greek methods. A Greek-speaking
person could pass from one end to the other without difficulty, and
we can understand how a knowledge of the whole tract of country
between the Adriatic and the Indus could be obtained by Greek scholars.
Alexander founded a large number of cities, all bearing his name, at
various points of his itinerary; but of these the most important
was that at the mouth of the Nile, known to this day as Alexandria.
Here was the intellectual centre of the whole Hellenic world, and
accordingly it was here, as we have seen, that Eratosthenes first
wrote down in a systematic manner all the knowledge about the habitable
earth which had been gained mainly by Alexander's conquests.

Important as was the triumphant march of Alexander through Western
Asia, both in history and in geography, it cannot be said to have
added so very much to geographical knowledge, for Herodotus was
roughly acquainted with most of the country thus traversed, except
towards the east of Persia and the north-west of India. But the
itineraries of Alexander and his generals must have contributed
more exact knowledge of the distances between the various important
centres of population, and enabled Eratosthenes and his successors
to give them a definite position on their maps of the world. What
they chiefly learned from Alexander and his immediate successors