Shiva Dhanush is the bow of lord Shiva. The same is considered to be very heavy and powerful. The person with divine blessings and purpose can get power to lift it and use it.This bow was given by Shiva to Janaka - father of janaki or Sita. The bow was kept as a test so that one who could string the bow would marry sita. Lord Rama broke the bow and married Sita