Legend says that when mother Earth was plundered upon by evil; especially by the ten headed King Ravana of Lanka, Lord Vishnu (one of the trinities in Indian mythology) took the avatar of Rama and was born as eldest son to King Dashratha and Queen Kaushalya of the kingdom of Ayodhya.
When Ravana took Devi Sita (Lord Ram’s eternal consort) by force to his kingdom, it was then that the battle of Lanka took place. To bring Sita back, Lord Ram fought with the evil Ravana and his forces with the aid of many of his trustees viz. Lord Hanuman, brother Lakshman, Ravana’s brother Vibhishan and an army of “Vanars” (literally meaning monkey). It was Ravana’s brother Vibhishan who eventually told the secret to kill Ravana, who was blessed by Lord Shiva that no man, no force, nor any arms would be able to kill him.
The secret was that Ravana can only be slayed by taking an aim at his navel.