The origin of the state of things here described is to be sought, according to the best authorities, in certain movements which took place about B.C. 200, in a remote region of inner Asia.  At that time a Turanian people called the Yue-chi were expelled from their territory on the west of Chen-si by the Hiong-nu, whom some identified with the Huns.  The Yue-chi separated into two bands; the smaller descended southwards into Thibet; the larger passed westwards, and after a hard struggle dispossessed a people called ‘Su’ of the plains west of the river of Hi.  These latter advanced to Ferghana and the Jaxartes; and the Yue-chi not long afterwards retreating from the Usiun, another nomadic race, passed the ‘Su’ on the north and occupied the tracts between the Oxus and the Caspian.  The Su were thus in the vicinity of the Bactrian Greeks; the Yue-chi in the neighborhood of the Parthians.  On the particulars of this account, which come from the Chinese historians, we cannot perhaps altogether depend; but there is no reason to doubt the main fact, attested by a writer who visited the Yue-chi in B.C. 139, that they had migrated about the period mentioned from the interior of Asia, and had established themselves sixty years later in the Caspian region.  Such a movement would necessarily have thrown the entire previous population of those parts into commotion, and would probably have precipitated them upon their neighbors.  It accounts satisfactorily for the pressure of the northern hordes at this period on the Parthians, Bactrians, and even the Indians; and it completely explains the crisis in Parthian history, which we have now reached, and the necessity which lay upon the nation of meeting and, if possible, overcoming, an entirely new danger.

In fact, one of those occasions of peril had arisen, to which in ancient times the civilized world was always liable from an outburst of northern barbarism.  Whether the peril has altogether passed away or not we need not here inquire; but certainly in the old world there was always a chance that civilization, art, refinement, luxury, might suddenly and almost without warning be swept away by an overwhelming influx of savage hordes from the unpolished North.  From the reign of Oyaxares, when the evil first showed itself, the danger was patent to all wise and far-seeing governors both in Europe and Asia, and was from time to time guarded against.  The expeditions of Cyrus against the Massagetse, of Darius Hystaspis against the European Scyths, of Alexander against the Getee, of Trajan and Probus across the Danube, were designed to check and intimidate the northern nations, to break their power, and diminish the likelihood of their taking the offensive.  It was now more than four centuries since in this part of Asia any such effort had been made; and the northern barbarians might naturally have ceased to fear the arms and discipline of the South.  Moreover the circumstances of the time scarcely left them a choice.  Pressed on continually