As per the text book rules of Vedic rites, as and when the solemn Horse sacrifice commenced, the Monarchs used to let loose a mighty horse to travel through the territories ruled by Royals of different races. Allowing the horse to run free and unhindered in their land shall be the symbolic gesture of the royals for accepting the supremacy of the master of Yahya, and subsequently become subordinate royals to the performer, those wish to defy dominance of the performer, block the free passage of the horse in their land to send the message ‘Let my flag flutter in my land, or you become my lord after conquering me'. The sacrifice horse thus dispatched by Rama, contained by the twins- Lava and Kusa, and held captive in hermit Valmiki’s ashram reached Rama’s ears and a wonder struck Rama inquired from the saintly sage through feelers as to who the twins were. The sage would not reveal the identity to the feelers, but promised to tear the mask once they render Ramayana in Rama's court at the end of the Yahya, till which time Rama need to restraint self and remain calm.
Sullied Rama lost his balance and on the counsel of sage Yathaajit, he transferred to Bharatha, his brother entire land of Sindhu, who too ruled it only for short while before bidding farewell to the rule and to position his sons Thakkan and Purlakan on Royal chair. Similar history followed with another brother Lakhman who too parted with the Kingship to throne Anghada and Chandrakethu his two sons. Not to be left behind, Rama too followed their steps to engage his twins in the ruling.
Thus Raghu brothers peacefully passed on their burden to their due and perfect successors to lead an austere life, and when the time to reach their lords in heaven came, the torch bearer in the form of sage Durvasa visited Rama. He desired one to one secret conference with Rama which when granted, met him in isolation and persuaded Rama to end his incarnation. Lashman, who stood guard at the gate broke in upon their secret conversation in a haste as he staggered to hear the content and turned sad. To atone the sin he committed by entering in secret meeting as uninvited guest, and fact on Rama’s end nearing heard, sad Lashman sought their pardon and in deep devotion and love to Rama quietly walked to river Sarayu in isolation and shed his earthly vesture in yogic style. The soul within his body flew to heaven.
One of the books, Valmiki Ramayana translated into Tamil, written in the year 1941 by an eminent author called ‘Maha Vidwan Sreemath Prathivathi Bayangaram Annangarachariya Swamigal’ of Kanjeepuram district of Tamilnadu in India has mentioned under title ‘Samshaeba Ramayana’ in the first Sarga of the book that it was Sage Narada who briefed the epic Ramayana to Valmiki and thereafter, the incident that provoked Valmiki in the bank of river Tamasa, prompted him to compose the Ramayana in verse form. As he was searching for suitable disciple to pass on the gem, Lava and Kusa came forward to absorb the epic.