The medicine of Sushruta is considerably older than the ninth century; and the grammar of Panini probably precedes Christianity. - Panini

Pāṇini's grammar defines Classical Sanskrit, so Pāṇini by definition lived at the end of the Vedic period. He notes a few special rules, marked chandasi ("in the hymns") to account for forms in the Vedic scriptures that had fallen out of use in the spoken language of his time. These indicate that Vedic Sanskrit was already archaic, but still a comprehensible dialect.

Panini, the ancient grammarian (probably belonged to 5th century or sixth century BC) mentions a character called Vasudeva son of Vasudeva, and also mentions Kaurava and Arjuna which testifies to Vasudeva Krishna, Arjuna and Kauravas being contemporaries. Megasthenes (350-290 BC), a Greek ethnographer and an ambassador of Seleucus I to the court of Chandragupta Maurya mentioned about Herakles in his famous work Indica. Many scholars have suggested that the deity identified as Herakles was Krishna

Among the earliest attempts to explain Pāṇini was the formulation of rules of interpretation or paribhāshās; a collection of these was made in the last century by Nāgojibhaṭṭa in his Paribhāshenduçekhara.