Did you know why Alexander did not proceed to conquer ancient Bengal?
At around 300 BC, when Alexander the great came to conquer Bengal—then known as Ganga Rashtra, meaning Nation on the River Ganges, alias Gangaridai—he abandoned the idea of going further considering the military strength of the then ruler. According to the account recorded by Roman writer Diodorus Siculus:
"When he (Alexander) moved forward with his forces certain men came to inform him that Porus, the king of the country, who was the nephew of that Porus whom he had defeated, had left his kingdom and fled to the nation of Gandaridai.
He had obtained from Phegeus a description of the country beyond the Indus: First came a desert which it would take twelve days to traverse; beyond this was the river called the Ganges which had a width of thirty two stadia, and a greater depth than any other Indian river; beyond this again were situated the dominions of the nation of the Prasioi and the Gandaridai, whose king, Xandrammes, had an army of 20,000 horse 200,000 infantry, 2,000 chariots and 4,000 elephants trained and equipped for war"....
"Now this (Ganges) river, which is 30 stadia broad, flows from north to south, and empties its water into the ocean forming the eastern boundary of the Gandaridai, a nation which possesses the greatest number of elephants and the largest in size."
That's right! That king had 4000 "trained" elephants! Imagine how many wild elephants we had back then.