The Vedas are the oldest remaining texts of the Indo-European tradition. The oldest text is called the Rig-Veda and was composed about 1500 BC. This text contains over 1000 hymns in praise of various gods (deva), among them Indra, Agni, Soma and many others. Soma, by the way, was also the name of a hallucinatory drink made from a plant.
The words in the Veda’s were considered absolutely authoritative and of supernatural origin. It was believed that they were not simply made up by their authors, but that they were heard (sruti) by seers (rishi). The syllables of the text, when spoken out loud, were considered sacred and powerful and sometimes even dangerous. In fact, only the brahmin (the priests), were allowed to speak them. They did so during rituals, which often contained altars, sacred fires and offerings of plants and animals to invoke the aid of the gods.
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