It is accepted that before going for the fight with Rama, Ravana saved his spirit with a recluse called Fire-Eye. The loner should watch Ravana's spirit and guard it until he returned for it. During the fight, Rama was astonished to see that none of the bolts that struck Ravana could hurt him. 

The mystery about Ravana's spirit was known to one of Rama's partners, who changed himself into Ravana and went to the recluse requesting to restore his spirit. 

As soon the spirit was liberated, Rama slaughtered the evil presence lord Ravana.