Several centuries ago, the Puru tribe’s expansion to the east and south, was led by two descendants of the illustrious Bharata - Devasravas and Devavata. On reaching the lake, they bathed there and reported feeling a sense of immediate rejuvenation and cleansing from within.
Then moving onto the banks of the Apaya, they performed a grand yagna (ritualistic prayer) asking their Gods to help them in their cause to spread in the new lands, to give them strong offspring who would spread even further and faster and finally to ensure their people had plenty of cattle and food at all times.
Author's Note: Rig Veda 03.023.04 is explicit in what the kings prayed for. (see Notes & References below).
They also vowed that the sacrificial fire kindled during the yagna would remain lit forever. A family of Angirasa priests were asked to take that responsibility and they became the first inhabitants of what came to be known as the Kaithal settlement.
Bharadvaja had chosen Kaithal settlement as the venue for holding the alliance talk. On reaching Kaithal, Bharadvaja, Srnjaya, Vadhryasva and Cayamana, took a dip in the Manusa lake. They then headed straight to pay homage to the Devavata fire as it had come to be known. As a further mark of their respect, they arranged to feed the entire priestly families who lived right next to the Apaya and constantly tended to the Devavata fire.
After lunch, the four, ensconced themselves in a simple yet cool mud dwelling offered to them by their priest hosts. For each man in the dwelling, there was a deep-rooted purpose for being there.
Here in the wasting fuel Jatavedas, eternal, hath assumed immortal being.
O Agni, look thou forth with ample riches: be, every day, bearer of food to feed us.
Praise Devavata's Agni, thou Devasravas, him who shall be the people's Lord.
On man, on Apaya, Agni! on the rivers Drsadvati, Sarasvati, shine richly.
To us be born a son and spreading offspring Agni, be this thy gracious will to us-ward