Pinaka was the bow that Sri Ram broke during the Swayamvara in the Ramayana to marry Sita. Pinaka, also written as Peenaka or Peenak, is the bow of God Shiva and He had gifted it to Parashuram, the incarnation of Vishnu. King Janaka of Mithila received it from Parashurama. One condition that was set by King Janaka for marrying Sita Devi was that the participant in the Swayamvara should lift the Pinaka bow and tie its string. Sri Ram lifted the bow and in his attempt to tie the string, the bow broke into two with a thunderous sound that shook the universe.
Legend has it that the Pinaka bow was gifted to Parashurama, the sixth Avatar (incarnation of Vishnu), by Shiva. Parashurama before going for deep meditation and austerities had given it to King Janaka for safe keeping.
Eight strong men were needed to move the Pinaka bow around. It is said that Child Sita Devi once while playing with her sisters had pushed the table around on which the Pinaka was placed.
King Janaka who saw this divine act decided that only a person who can lift and tie the string of the Pinaka bow would be the fit person to marry Sita Devi.
This feat was accomplished by Sri Ram during the Sita Swayamvara.
Later an angry Parashuram confronted Sri Ram and challenged him for breaking the Pinaka. But the calmness and the smile of Sri Ram melted the anger of Parashuram who soon realized that the Ram before him is no ordinary man. Parashuram then gave blessings to the new couple and went away to do His Tapas and austerities.