creases of population; then two or three hard years would suffice to send the tribes wandering again in search of food.
From before the dawn of recorded history this region of human accumulation between the Danube and China had been, as it were, intermittently raining out tribes southward and westward. It was like a cloud bank behind the settled landscape that accumulated and then precipitated invaders. We have noted how the Keltic peoples drizzled westward, how the Italians, the Greeks, and their Epirote, Macedonian, and Phrygian kindred came south. We have noted too the Cimmerian drive from the east, like a sudden driving shower of barbarians across Asia Minor, the southward coming of the Scythians and Medes and Persians, and the Aryan descent into India. About a century before Alexander there had been a fresh Aryan invasion of Italy by a Keltic people, the Gauls, who had settled in the valley of the Po. Those various races came down out of their northern obscurity into the light of history; and meanwhile beyond that light the reservoir accumulated for fresh discharges. Alexander's march in Central Asia brings now into our history names that are fresh to us; the Parthians, a race of mounted bowmen who were destined to play an important rôle in history a century or so later, and the Bactrians who lived in the sandy native land of the camel. Everywhere he seems to have met Aryan-speaking peoples. The Mongolian barbarians to the north-eastward were still unsuspected, no one imagined there was yet another great cloud bank of population beyond the Scythians and their kind, in the north of China, that was presently also to begin a drift westward and southward, mixing as it came with the Nordic Scythians and every other people of kindred habits that it encountered. As yet only China knew of the Huns; there were no Turks in Western Turkestan or anywhere else then, no Tartars in the world.
This glimpse of the state of affairs in Turkestan in the fourth century B.C. is one of the most interesting aspects of the wanderings of Alexander; another is his raid through the Punjab. From the point of view of the teller of the human story it is provocative that he did not go on into the Ganges country, and that consequently we have no independent accounts by Greek writers of the life in ancient Bengal. But there is a considerable literature in