This is a historical quote, not one from a movie, but it's one I've always found chilling.

If I'm remembering this right sometimes when Mongols would besiege a town they would ask for it's surrender. Sometimes they would kill most of the inhabitants and enslave the rest anyway, sometimes they were more merciful. But if you resisted at all essentially everyone would die.

The quote essentially said that if they didn't surrender completely and immediately they would "...have the same fate as a stone dropped in deep water."

I always thought of these cities just being erased from existence with all their inhabitants, and no one ever living who remembered it - Mongols did on occasion go so far as to take down every stone from a city's walls and cart them off, seemingly just out of spite.