Matsya Purana — The Kauśika Descendants: Śrāddha
तथैकमतिथिं कृत्वा श्राद्धदः स्वयमेव तु चकार मन्त्रवच्छ्राद्धं स्मरन्पितृपरायणः //
tathaikamatithiṃ kṛtvā śrāddhadaḥ svayameva tu cakāra mantravacchrāddhaṃ smaranpitṛparāyaṇaḥ //
Thus, having fixed a single proper tithi, the performer of the Śrāddha himself carried it out in accordance with the mantras, remembering the ancestors and devoted to the Pitṛs.
This verse does not address pralaya; it focuses on dharma—specifically the correct performance of śrāddha on an appointed tithi with mantra-precision and remembrance of the Pitṛs.
It highlights pitṛkārya as a core duty: selecting an appropriate lunar day (tithi), performing śrāddha personally, and maintaining ancestral devotion—an ideal expected of householders and rulers alike in Purāṇic dharma.
The significance is ritual (not architectural): śrāddha should be performed on a properly fixed tithi and executed “mantravat,” i.e., with correct Vedic/Purāṇic mantras and disciplined procedure.