and the knowledge of silver goes hand in hand with that of iron, owing to the manner in which these metals are intermingled in the ore which produces them. These two metals, moreover, are not found in any quantity in the north-west of India.
The evidence of the topography, the climate, and the products of the country thus shows that the people by whose poets the Rigveda was composed were settled in the north-west of India, from the Kabul to the Jumna. But they were still engaged in conflict with the aborigines, for many victories over them are referred to. Thus Indra is said to have bound 1000 or slain 30,000 of them for his allies. That the conquerors were bent on acquiring new territory appears from the rivers being frequently mentioned as obstacles to farther advance. The invaders, though split up into many tribes, were conscious of a unity of race and religion. They styled themselves Āryas or "kinsmen," as opposed to the aborigines, to whom they gave the name of Dasyu or Dāsa, "fiends," in later times also called anārya, or non-Aryans. The characteristic physical difference between the two races was that of colour (varṇa), the aborigines being described as "black" (kṛishṇa) or "black-skins," and as the "Dāsa colour," in contrast with the "Aryan colour" or "our colour." This contrast undoubtedly formed the original basis of caste, the regular name for which in Sanskrit is "colour."
Those of the conquered race who did not escape to the hills and were captured became slaves. Thus one singer receives from his royal patron a hundred asses, a hundred sheep, and a hundred Dāsas. The latter word in later Sanskrit regularly means servant or slave, much in the same way as "captive Slav" to the German
