Matsya Purana — The Observance of Ananta-Tritiya
नभस्ये वाथ वैशाखे पुण्यमार्गशिरस्य च शुक्लपक्षे तृतीयायां सुस्नातो गौरसर्षपैः //
nabhasye vātha vaiśākhe puṇyamārgaśirasya ca śuklapakṣe tṛtīyāyāṃ susnāto gaurasarṣapaiḥ //
In the month of Nabhasya, or in Vaiśākha, and also in the auspicious month of Mārgaśīrṣa—on the third lunar day (tṛtīyā) of the bright fortnight—one should bathe thoroughly, using yellow (golden) mustard seeds.
This verse does not discuss pralaya; it focuses on vrata-dharma—timing and method of ritual purification (snāna) for merit.
It gives a practical dharma guideline: on specified auspicious months and the bright-fortnight Tṛtīyā, a disciplined person (including householders and rulers) should perform proper bathing as part of regular religious observance and self-purification.
The significance is ritual, not architectural: it prescribes snāna on Śukla Tṛtīyā using yellow mustard seeds, a traditional purifier used in cleansing rites.