For instance, the Aryans, spreading and pressing westward in successive waves of Keltic-speaking peoples through Gaul and Britain and Ireland, mixed more and more with Iberian races, and were affected more and more by that Iberian blood and their speech by the characteristics of the language their Keltic tongue superseded. Other waves of Keltic peoples washed with diminishing force into Spain and Portugal, where to this day the pre-Keltic strain is altogether dominant although the languages spoken are Aryan. Northward, in Europe, the Aryan peoples were spreading into hitherto uninhabited country, and so remaining racially more purely Nordic blonds. They had already reached Scandinavia many centuries b.c.
From their original range of wandering, other Aryan tribes spread to the north as well as to the south of the Black Sea, and ultimately, as these seas shrank and made way for them, to the north and east of the Caspian, and so began to come into conflict with and mix also with Mongolian peoples of the Ural-Altaic linguistic group, the horsekeeping people of the grassy steppes of Central Asia. From these Mongolian races the Aryans seem to have acquired the use of the horse for riding and warfare. There were three or four prehistoric varieties or sub-species of horse in Europe and Asia, but it was the steppe or semi-desert lands that first gave horses of a build adapted to other than food uses. All these peoples, it must be understood, shifted their ground rapidly, a succession of bad seasons might drive them many hundreds of miles, and it is only in a very rough and provisional manner that their "beats" can now be indicated. Every summer they went north, every winter they swung south again. This annual swing covered sometimes hundreds of miles. On our maps, for the sake of simplicity, we represent the shifting of nomadic peoples by a straight line; but really they moved in annual swings, as the broom of a servant who is sweeping out a passage swishes from side to side as she advances. Spreading round the north of the Black Sea, and probably to the north of the Caspian, from the range of the original Teutonic tribes of Central and North-central Europe to the Iranian peoples who became the Medes and Persians and (Aryan) Hindus, were the grazing lands
- Roger Pocock's Horses is a good and readable book on these questions.