Meanwhile the usual process had been going on in Greece by which a country becomes consolidated. From time to time one of the tribes into which that mountainous country was divided, obtained supremacy over the rest: at first the Athenians, owing to the prominent part they had taken in repelling the Persians; then the Spartans, and finally the Thebans. But on the northern frontiers a race of hardy mountaineers, the Macedonians, had consolidated their power, and, under Philip of Macedon, became masters of all Greece. Philip had 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
