Śrīmad-Bhāgavatam · Text 9.13.18
Who is speaking and story frame
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
From Hrasvaromā came a son named Śīradhvaja [also called Janaka]. When Śīradhvaja was plowing a field, from the front of his plow [śīra] appeared a daughter named Sītādevī, who later became the wife of Lord Rāmacandra. Thus he was known as Śīradhvaja.
Read this verse on Vedabase.ioThis verse has no purport; its meaning is explained by the verses around it.