The migrations of nomadic peoples in the second century BCE threatened two great civilizations—Hellenistic Bactria and Han China.In the end, Zhang Qian of the latter bore witness to the collapse of the former.Thus, while China endured, the Greeks failed in Asia.Why? Old theories focus upon the ill-timed exhaustion of Bactrian resources in the conquest of India, or the endless infighting among rival Greek dynasts, or simply the inevitability of numbers as waves of barbarians washed over Bactria.These explanations are insufficient.This paper proposes that the power of the Greeks in Bactria was never as strong as moderns have imagined it to be.The illusion of strength conveyed to us by kings with grandiose titles, over-sized coinages, and impressive cities (such as Ai Khanoum) was just that—a bold deception engineered by the Greeks to mask their own weaknesses.This strategy is here called the Beas Effect because of the legend that Alexander the Great created a false sense of Greek might by setting up a massively over-sized encampment at the Beas River to intimidate those outside his empire.Hellenistic Bactria likewise projected power disproportionate to reality, explaining why the state crumbled so quickly and completely.