This short enumeration of the various tribes near the Euxine and the Caspian, as well as we can make them out, from the seventh to the fifth century B. C., is necessary for the comprehension of that double invasion of Scythians and Cimmerians which laid waste Asia between 630 and 610 B. C. We are not to expect from Herodotus, born a century and a half afterwards, any very clear explanations of this event, nor were all his informants unanimous respecting the causes which brought it about. But it is a fact perfectly within the range of historical analogy, that accidental aggregations of number, development of aggressive spirit, or failure in the means of subsistence, among the nomadic tribes of the Asiatic plains, have brought on the civilized nations of southern Europe calamitous invasions, of which the prime moving cause was remote and unknown. Sometimes a weaker tribe, flying before a stronger, has been in this manner precipitated upon the territory of a richer and less military population, so that an impulse originating in the distant plains of Central Tartary has been propagated until it reached the southern extremity of Europe, through successive intermediate tribes, a phenomenon especially exhibited during the fourth and fifth centuries of the Christian era, in the declining years of the Roman empire. A pressure so transmitted onward is said to have brought down the Cimmerians and Scythians upon the more southerly regions of Asia. The most ancient story in explanation of this incident seems to have been contained in the epic poem (now lost) called _Arimaspia_, of the mystic Aristeas of Prokonnêsus, composed apparently about 540 B. C. This poet, under the inspiration of Apollo,[470] undertook a pilgrimage to visit the sacred Hyperboreans (especial votaries of that god) in their elysium beyond the Rhipæan mountains; but he did not reach farther than the Issêdones. According to him, the movement, whereby the Cimmerians had been expelled from their possessions on the Euxine sea, began with the Grypes or Griffins in the extreme north,—the sacred character of the Hyperboreans beyond was incompatible with aggression or bloodshed. The Grypes invaded the Arimaspians, who on their part assailed their neighbors the Issêdones;[471] these latter moved southward or westward and drove the Scythians across the Tanais, while the Scythians, carried forward by this onset, expelled the Cimmerians from their territories along the Palus Mæotis and the Euxine. [470] Herodot. iv, 13. φοιβολαμπτὸς γενομένος. [471] Herodot. iv, 13.