THE YUEH-CHI MIGRATION 221 pied them. The Sakas were forced to migrate in search of new quarters, and, ultimately, as stated in the last preceding chapter, made their way into India and Sistan. For some fifteen or twenty years the Yueh-chi re- mained undisturbed in their usurped territory. But meantime their ancient enemies, the Hiung-nu, had protected the infant son of the slain Wu-sun chieftain, who had grown to manhood under their care. This youth, with Hiung-nu help, attacked the Yueh-chi, and avenged his father's death by driving them from the lands which they had wrested from the Sakas. Being thus forced to resume their march, the Yueh-chi moved into the valley of the Oxus, and reduced to subjection its peaceful inhabitants, known to the Chinese as Ta- hia. The political domination of the Yueh-chi was probably extended at once over Bactria, to the south of the Oxus, but the headquarters of the horde con- tinued for many years to be on the north side of the river, and the pastures on that side sufficed for the wants of the newcomers. In the course of tune, which may be estimated at two or three generations, the Yueh-chi lost their nomad habits, became a settled, territorial nation, in actual occupation of the Bactrian lands south of the river, as well as of Sogdiana to the north, and were divided into five principalities. As a rough approximation to the truth, this political and social development, with its accompanying growth of population, may be assumed to have been completed about 70 B. c.