Ravana the King of Lanka Kidnapped Sita , the wife of Sri Ram as a Revenge for his Sister Sooparnakha , who wants to marry Sri Ram, and her nose was cut by Lakshmana to teach her a lesson.
Sri Ram and Lakshman along with army of Sughreeva and hanuman came to rescue her. to reach lanka they had to cross the vast ocean and reach Lanka. Sri Ram ordered the Ocean to leave his way but the ocean showed no sign . Sri Ram pulled a bow to dry the Ocean , as to teach the arrogant ocean a lesson. The Ocean prayed to Sri Ram to under stand that he was bound to stay at his position and he must pray to Lord Shiva for the solution. Raam has already set the arrow in the bow , he asked the Ocean where else could he shoot the arrow if not at him , Ocean suggested a useless barren dweep ( small island) which lies on the way to Lanka. Raam shoot the arrow at it, its now called as Dhanushkodi, and made it fertile.