The Killing of the Demon Ravana
Ravana, who had ten arms and ten heads, was the wicked king of the island of Sri Lanka, who kidnapped the wife of Rama. Rama had been in exile for 14 years because of a disagreement as to whether he or his brother should be the next king in Ayodhya.
After a great battle Rama killed the demon and recovered his wife. Rama's return with his wife Sita to Ayodhya and his subsequent coronation as king is celebrated at Diwali.
When Rama and Sita first returned to Ayodhya it was a dark moonless night and they couldn't see where they were going. Their people put little lamps outside their houses so that the new king and queen could find their way.