On this occasion we celebrate that Lord Ramacandra won over the king of the demons, Ravana. This year's date is the following: 30th September (Saturday), 2017.
"Lord Rāmacandra, surrounded by Lakṣmaṇa and monkey soldiers like Sugrīva, Hanumān, Gandhamāda, Nīla, Aṅgada, Jāmbavān and Panasa, attacked the soldiers of the Rākṣasas, who were fully equipped with various invincible weapons like swords, lances, bows, śakti arrows, ect." (Srimad-Bhagavatam, 9.10.19.)
"Lord Rāmacandra said to Rāvaṇa: You are the most abominable of the man-eaters... You resemble a dog, for as a dog steals eatables from the kitchen in the absence of the householder, in My absence you kidnapped My wife, Sītādevī. Therefore as Yamarāja punishes sinful men, I shall also punish you. You are most abominable, sinful and shameless... After thus rebuking Rāvaṇa, Lord Rāmacandra fixed an arrow to His bow, aimed at Rāvaṇa, and released the arrow, which pierced Rāvaṇa’s heart like a thunderbolt." (Srimad-Bhagavatam, 9.10.22-23.)