How does Rama finally kill ravana?

Ram's army had build a huge bridge between Lanka and the mainland. They crossed the ocean and attacked Ravana's army. During the battle, Lakshmana was heavily wounded, but he was cured by a magic herb which Hanuman flew all the way to the Himalayas to obtain. Not finding the herb at first, Hanuman brought the entire mountain just to be sure. Finally, all rakshasa generals were killed and the battle become a single combat between Ravana and Ram. Finally, Ram killed Ravana with a special weapon given to him by saint Agastya.,debashis sahoo. debashis sahoo