tatah siradhvajo jajne
yajnartham karsato mahim
sita siragrato jata
tasmat siradhvajah smrtah
tatah—from Hrasvaroma; siradhvajah—a son named Siradhvaja; jajne—was born; yajna-artham—for performing sacrifices; karsatah—while plowing the field; mahim—the earth; sita—mother Sita, the wife of Lord Ramacandra; sira-agratah—from the front portion of the plow; jata—was born; tasmat—therefore; siradhvajah—was known as Siradhvaja; smrtah—celebrated.
From Hrasvaroma came a son named Siradhvaja [also called Janaka]. When Siradhvaja was plowing a field, from the front of his plow [sira] appeared a daughter named Sitadevi, who later became the wife of Lord Ramacandra. Thus he was known as Siradhvaja.
Link to this page: https://prabhupadabooks.com/sb/9/13/18