The cause of the sudden growth of Media in power about this period, and of the consolidation which followed rapidly upon that growth, is to be sought, apparently, in fresh migratory movements from the Arian head-quarters, the countries east and south-east of the Caspian.  The Cyaxares who about the year B.C. 632 led an invading host of Medes against Nineveh, was so well known to the Arian tribes of the north-east that, when in the reign of Darius Hystaspis a Sagartian raised the standard of revolt in that region he stated the ground of his claim to the Sagartian throne to be descent from Cyaxares.  This great chief, it is probable, either alone, or in conjunction with his father (whom Herodotus calls Phraortes), led a fresh emigration of Arians from the Bacterian and Sagartian country to the regions directly east of the Zagros mountain chain; and having thus vastly increased the strength of the Arian race in that quarter, set himself to consolidate a mountain kingdom capable of resisting the great monarchy of the plain.  Accepted, it would seem, as chief by the former Arian inhabitants of the tract, he proceeded to reduce the scattered Scythic tribes which had hitherto held possession of the high mountain region.  The Zimri, Minni, Hupuska, etc., who divided among them the country lying between Media Proper and Assyria, were attacked and subdued without any great difficulty; and the conqueror, finding himself thus at the head of a considerable kingdom, and no longer in any danger of subjugation at the hands of Assyria, began to contemplate the audacious enterprise of himself attacking the Great Power which had been for so many hundred years the terror of Western Asia.  The supineness of Asshur-bani-pal, the Assyrian king, who must at this time have been advanced in years, encouraged his aspirations; and about B.C. 634, when that monarch had held the throne for thirty-four years, suddenly, without warning, the Median troops debouched from the passes of Zagros, and spread themselves over the rich country at its base, Alarmed by the nearness and greatness of the peril, the Assyrian king aroused himself, and putting himself at the head of his troops, marched out to confront the invader.  A great battle was fought, probably somewhere in Adiabene, in which the Medes were completely defeated:  their whole army was cut to pieces; and the father of Cyaxares was among the slain.  Such was the result of the first Median expedition against Nineveh.  The assailants had miscalculated their strength.  In their own mountain country, and so long as they should be called upon to act only on the defensive, they might be right in regarding themselves as a match for the Assyrians; but when they descended into the plain, and allowed their enemy the opportunity of manoeuvering and of using his war chariots, their inferiority was marked.  Cyaxares, now, if not previously, actual king, withdrew awhile from the war, and, convinced that all the valor of his Medes would be unavailing