"Although no data as such are available for the ancient times, there are statements of Greek writers which depict India as a country of large population. Apollodorus writes that there were between Hydaspes (Jhelum) and Hyphasis (Beas)—approximately the kingdom of Porus—1500 cities, none of which was less than a kos, which, adds Elphinstone, ‘with every allowance for exaggeration, supposes a most flourishing territory‘."
January 1, 1970
https://en.wikiquote.org/wiki/Demographics_of_India