No conclusive explanation can be offered as to how this remarkable change took place in the course of the centuries embraced by the Vedic period. It may have been due primarily to sectarian strife between the religious teachers of those tribes which had been influenced by Babylonian modes of thought and those which clung tenaciously to the forms of primitive Aryan nature worship, and perhaps also the worship of ancestors (Pitris). In the old Persian language, which, like Greek, places “h” before a vowel where “s” is used in Sanskrit, Ahura ( = Asura) signifies “god”. The Zoroastrian chief god is called Ahura-Mazda, “the wise Lord”, as Varuna is addressed in early Rigvedic hymns, “wise Asura and King”, and “the all-knowing Asura who established the heavens and fixed the limits of the earth”. On the other hand “daeva” in the Iranian dialect, which is cognate with Sanskrit “deva”, “god”, came to mean “demon”. “Asura” is derived from the root “asu”, which signifies “the air of life”, and “deva” from “div”, “to shine”, or “deiwo”, “heavenly”. The view has been urged that the revolt against “Asura” in India was due to the hatred cherished towards the Persians who had become subject to the Assyrians, the worshippers of Ashur. It was originally based on the assumption that Assyrian aggression caused the migration of Aryan tribes towards India. Subsequent research, however, has tended to dispel this theory. It has been found, for instance, that Aryans were associated with the Kassites who overthrew the Hammurabi dynasty of Babylon prior to the invasion of the Punjab, and that the Assyrians were for a period vassals of the Mitanni kings, who had Aryan names and worshipped Indra, Varuna, and Mithra in Mesopotamia and Asia Minor. The weak point in the Ashur-Asura theory is that it throws no light on the process which caused the Persian “daeva” to be applied to demons instead of to gods. How the gods of the Indian Aryans became the demons of Persia and the demons of Persia became the gods of India is a problem for which a solution has yet to be found. The expository and speculative books of the priests—the _Brahmanas_ and _Upanishads_—which are attached to the Vedic hymns, do not help us greatly in accounting for the change. We read that “the gods and Asuras contended together, and that the former, being less numerous than the latter, took some bricks, and placing them in a proper position to receive the sacrificial fire, with the formula, ‘Thou art a multiplier’, they became numerous”.[113] In one of the Brahmanas we are informed: [113] Muir's _Original Sanskrit Texts_, v, 15.