The Cambridge History of India, Vol. I: Ancient India v1.c31.15

v1.c31.15

These three settlements are no doubt merely specimens of the larger deposits left by the waves of Scythian migration which may be traced back in history to about the middle of the eighth century B.C. The flood had now for some three and a half centuries been held in check by the barrier maintained in Bactria, first by the Achaemenid kings of Persia and afterwards by the successors of Alexander. But the strength of Bactria had been sapped by foreign and domestic strife, and it was no longer capable of resisting the pressure of barbarian hordes on the frontier.