Panini, the grammarian of India, was said to be contemporary with King Nanda, who was the successor of Chandragupta, the contemporary of Alexander, and therefore in the second half of the fourth century before Christ.

Dates are so precarious in Indian literature, says Max Mueller, that a confirmation within a century or two is not to be despised.

Now the grammarian Katyayana completed and corrected the grammar of Panini, and Patanjeli wrote an immense commentary on the two which became so famous as to be imported by royal authority into Cashmere, in the first half of the first century of our era.

Mueller considers the limits of the Sutra period to extend from 600 B.C.to 200 B.C.Buddhism before Asoka was but modified Brahmanism.

The basis of Indian chronology is the date of Chandragupta.
All dates before his time are merely hypothetical.