the gods would not allow such defiance. hermes, the messenger god in greek mythology, forced sisyphus to return to the underworld. the gods had planned a suitable punishment for him: they would let him live, but he was to live a meaningless life. for all eternity he would have to push a rock up a mountain, knowing that the rock would roll back down as soon as he reached the top.

roll down이 굴러 떨어지다 이고, back은 부사로 보이는데.. roll back down 이라고 쓴 이유가 뭔가요?