Sumantra, urged to speed away, The townsmen’s call must disobey, Forth as the long-armed hero went, The dust his chariot wheels up sent Was laid by streams that ever flowed From their sad eyes who filled the road.

In plain words: Sumantra, the royal charioteer, has to ignore the people begging him to stop and drives Rama away. So many people cry along the road that their tears settle the dust kicked up by the chariot wheels.