Vedic Sanskrit was an ancient language of the Indo-Aryan subgroup of the Indo-European languages. It is attested in the Vedas, texts compiled over the period of the mid-2nd to mid-1st millennium BCE. It was orally preserved, predating the advent of Brahmi script by several centuries.
Extensive ancient literature in the Vedic Sanskrit language has survived into the modern era, and this has been a major source of information for reconstructing Proto-Indo-European and Proto-Indo-Iranian history. Quite early in the pre-historic era, Sanskrit separated from the Avestan language, an Eastern Iranian language. The exact century of separation is unknown, but this separation of Sanskrit and Avestan occurred certainly before 1800 BCE. The Avestan language developed in ancient Persia, was the language of Zoroastrianism, but was a dead language in the Sasanian period. Vedic Sanskrit developed independently in ancient India, evolved into classical Sanskrit after the grammar and linguistic treatise of Pāṇini, and later into many related Indian subcontinent languages in which are found the voluminous ancient and medieval literature of Buddhism, Hinduism and Jainism.
The separation of proto-Indo-Iranian language into Avestan and Vedic Sanskrit is estimated, on linguistic grounds, to have occurred around or before 1800 BCE. The date of composition of the oldest hymns of the Rigveda is vague at best, generally estimated to roughly 1500 BCE. Both Asko Parpola (1988) and J. P. Mallory (1998) place the locus of the division of Indo-Aryan from Iranian in the Bronze Age culture of the Bactria–Margiana Archaeological Complex (BMAC). Parpola (1999) elaborates the model and has "Proto-Rigvedic" Indo-Aryans intrude the BMAC around 1700 BCE. He assumes early Indo-Aryan presence in the Late Harappan horizon from about 1900 BCE, and "Proto-Rigvedic" (Proto-Dardic) intrusion to the Punjab as corresponding to the Gandhara grave culture from about 1700 BCE. According to this model, Rigvedic within the larger Indo-Aryan group is the direct ancestor of the Dardic languages.
The early Vedic Sanskrit language was far less homogenous, and it evolved over time into a more structured and homogeneous language. The language in the early Upanishads of Hinduism and the late Vedic literature approaches Classical Sanskrit, states Gombrich. The formalization of the late Vedic Sanskrit language into the Classical Sanskrit form is credited to Pāṇini, along with Patanjali's Mahabhasya and Katyayana's commentary that preceded Patanjali's work.
Vedic differs from Classical Sanskrit to an extent comparable to the difference between Homeric Greek and Classical Greek. Tiwari ( 2005) lists the following principal differences between the two: