Nimi’s Disembodied Liberation and the Rise of the Mithilā (Videha) Dynasty
तत: शीरध्वजो जज्ञे यज्ञार्थं कर्षतो महीम् । सीता शीराग्रतो जाता तस्मात् शीरध्वज: स्मृत: ॥ १८ ॥
tataḥ śīradhvajo jajñe yajñārthaṁ karṣato mahīm sītā śīrāgrato jātā tasmāt śīradhvajaḥ smṛtaḥ
Then from Hrasvaromā was born a son named Śīradhvaja, also known as Janaka. While plowing the earth for the sake of yajña, from the very front of his plow Sītādevī appeared; therefore he was remembered as Śīradhvaja.
This verse states that Sītā manifested from the very tip of the plough while the king was ploughing the earth for the purpose of a yajña.
Because Sītā appeared from the plough (śīra), and due to that event he became known and remembered as Śīradhvaja.
It highlights sacred intention in work—when actions are done as an offering (yajña-bhāva), divine outcomes and blessings arise in unexpected ways.