The religious books of India are written in Sanskrit, the tongue of Aryan conquerors who came into India across the northwestern mountains nearly two thousand years before Christ. The Aryans brought with them the worship of the powers of nature, the “devas,” or bright ones. From the Rig-Veda, or collection of hymns to various gods, which were composed for the worship of the Aryans during the earliest centuries of their dwelling in India, we learn something about these deities. Some were simply forces of nature, such as Father Heaven, Mother Earth, the Dawn Goddess, the Sun God, and the Wind God. With other deities new trains of ideas became connected that tended to obscure their original character. The Fire God, for instance, personified the fire of sacrifice and domestic use, the atmospheric fire of lightning, and sometimes even the sun. Thus he became the priest, mediating between man and the gods. Similarly Varuna, who at first apparently typified the open sky, whose eye is the sun, subsequently grew into a mighty guardian of the laws of nature and morality. This earliest age of Hinduism, the age to which the Rig-Veda belongs, is known as the Vedic Age, and the gods of this age were worshipped with sacrifice. In the Vedic period Aryan society probably divided itself into the soldier-yeoman and the priest. The soldier and yeoman, desirous of winning the goodwill and active assistance of the gods of the sky and earth, would hire the priest, who thus came to be regarded as the master of the rites which cajole or constrain the invisible powers. As the Aryans extended their sway over India, the influence of the Brahmans or priests increased, and in their hands religion underwent a profound change. Personal worship gave way to ecclesiastical ritualism. The idea of sacrifice as a means of compelling the gods grew to an enormous degree, and the welfare of the world was imagined to depend upon ritual, the key to which was in the hands of the Brahmans.