Shiva Dhanush (Sanskrit: शिव धनुश), also known as Pinaka(Ajagav), in Hindu mythology, was the divine bow of Lord Shiva gifted to King Janaka by Sage Parashurama for safe-keeping while the sage performed penances. It was gifted to Parashurama by Shiva for being a great disciple. The bow is 8.5 feet in length as mentioned in the Dhanurveda.
In earlier part of her life, Sita while playing with her sisters had unknowingly moved the table over which the "Shiva Dhanush" had been placed; which was something no one in the palace could do. This incident was however observed by King Janaka and he decided to make this incident as the backdrop for swayamvar.
Later, Janaka had announced that whoever wanted to marry Sita had to do so only after lifting (which was itself a difficult job) the bow from its place and stringing it. The bow was broken by Lord Rama when he attempted to string the bow, during the swayamvar of King Janaka's daughter, Sita, whereby he won the hand of Sita in marriage. After the swayamvar, while Rama, Sita and Lakshmana were on their way to Ayodhya, Parashurama confronted and challenged Rama for breaking the bow. Dasharatha told Parashurama the incident which had happened in the palace. But Parashurama wouldn't control and brought Lord Vishnu's bow. He then asked Rama to string the bow and fight a duel with him.Rama respectfully bows to Parashurama, and within a twinkling of an eyelid snatches the bow of Vishnu, strings it, places an arrow and points it straight at the challenger's heart. Rama asks Parashurama what he will give as a target to the arrow in return for his life? At this point, Parashurama feels himself devoid of the tremendous mystical energy he possessed for so long. He realizes that Rama is Vishnu incarnate, his successor and definitely his superior. He accepts Rama's superiority, devotes his tapasya to him, pays homage to Rama and promises to return to his hermitage and leave the world of men.
Rama then shoots the arrow up into the sky with Vishnu's bow, performing a feat true to his supreme, divine nature with his natural weapon. His overpowering of Parashurama and using the supreme weapon with ease. Then Parashurama left this world to mahendra Parvat.