Yudha Kanda (The Book of war or Lanka Kanda) is the fourth book of the Valmiki Ramayana, which is one of the two great epic poems of India, the other being the Mahabharata. The book consists of 128 sargas (sometimes translated as chapters or cantos) of Sanskrit verse.
This Yudha Kanda also known as Lanka kanda, this book describes the battle between the army of Rama, constructed with the help of Sugriv and Ravana. Having received Hanuman’s report on Sita, Rama and Lakshmana proceed with their allies toward’s the shore of the southern sea. There they are joined by Ravana’s renegade brother Vibhishana. The monkey’s named Nala and Nila construct a floating bridge (known as Rama Setu) across the ocean, and the princes and their army cross over to Lanka. A lengthy battle ensues and Rama kills Ravana. Rama then installs Vibhishana on the throne of Lanka.
On meeting Sita, Rama asks her to undergo an “agni pariksha” (test of fire) to prove her purity, as he wanted to get rid of the rumours surrounding Sita’s purity. When Sita plunges into the sacrificial fire, Agni the lord of fire raises Sita, unharmed, to the throne, attesting to her purity. The episode of agni pariksha varies in the versions of Ramayana by Valmiki and Tulsidas. The above version is from Valmiki Ramayana. In Tulsidas’s Ramacharitamanas Sita was under the protection of Agni (see Maya Sita) so it was necessary to bring her out before reuniting with Rama. At the expiration of his term of exile, Rama returns to Ayodhya with Sita and Lakshmana, where the coronation is performed. This is the beginning of Ram Rajya, which implies an ideal state with good morals.