Once upon a time, there lived a great King called Sagara. He is believed to have sixty thousand sons and is considered the originator of the Ikshvaku dynasty. In this illustrious lineage was born King Dasharatha, son of King Raghu and grandson of King Dilipa. He had three wives- Kaushalya, Sumitra and Kaikeyi. He ruled over the prosperous kingdom of Kosala, on the riverbanks of Sarayu, with the city of Ayodhya as its capital.
According to the legend, Ayodhya was built by Manu, the foremost ruler of mankind. That magnificent city had well laid out and well maintained highways, and was surrounded with gateways and arches. It housed all kinds of machinery, weaponry and craftsmen. It had a rich cultural heritage and was overflowing with food and clean water. There was an abundance of livestock and wealth amongst its residents.
King Dasharatha remained childless for a long time and finally decided to perform the Ashwamedha Yagna (a Vedic Horse Ritual) in order to beget heirs to his kingdom. After consulting his ministers, priests and noblemen, it was decided to perform the yagna on the northern banks of river Sarayu. The preparations began under the supervision of the royal priest, Sage Vasishtha. As per the custom, a well-decorated horse was let out with an insignia on its forehead, challenging any king to capture it and to face the wrath of the king releasing it. If someone captured the horse, he would have to fight Dasharatha, else the valor and invincibility of Dasharatha would be well established and he would proceed with the Ashwamedha ritual after a year. So, when the horse came back without being captured, the final rituals of the Ashwamedha yagna, including the Putra Kameshthi yagna were performed.
The Gods were very pleased with the rituals and Vishnu agreed to incarnate as a human, by being born as Dasharatha’s son. During the Putra Kameshthi yagna, Prajaapatya Purusha arose from the sacrificial fire and gave a golden vessel of divine dessert to Dasharatha for distribution to his three queens. Upon consuming the divine dessert, the queens conceived four sons. Rama, the eldest son was born to Kausalya, Bharata was born to Kaikeyi, and Lakshmana and Shatrughna were born to Sumitra.