Which areas in India specifically remained citadels of Hinduism even during the Buddhist-Jain peak periods (from the time of their inception to the emergence of the Guptas). How did these areas remain strongly adhering to Hinduism? What kept them insulated? I ask this because when I read the history of the time what stands out is that both these faiths spread far and wide in the subcontinent. So I wonder if there were any places they could not penetrate due to strong Hindu presence?