The Indian River Basin, also known as the Ganga River Basin is bounded by the Himalays in the North and the Vindhya Range to the South.
The vindhya are technically, not a single mountain range but a more complex and mostly discontinous chains of hills and mountains.
They have traditionally defined the gap between North India and South India and thus, have a huge place in the country's mythology.
In ancient times, they were usually seen as dangerous and not easy to pass due to the dense vegetation in the area.