Matsya Purana — Yuga Durations
द्वाभ्यामधर्मः पादाभ्यां त्रिभिर्धर्मो व्यवस्थितः यत्र सत्यं च सत्त्वं च त्रेताधर्मो विधीयते //
dvābhyāmadharmaḥ pādābhyāṃ tribhirdharmo vyavasthitaḥ yatra satyaṃ ca sattvaṃ ca tretādharmo vidhīyate //
In the Tretā age, adharma stands on two feet, while dharma is established on three. There, truthfulness and purity of being (sattva) prevail—thus the dharma of Tretā is ordained.
It does not describe pralaya directly; instead, it outlines cosmic moral order across ages, showing how dharma declines by “legs/feet” as yugas progress—an ethical framework often paired with larger cycles of creation and dissolution.
By highlighting satya (truthfulness) and sattva (purity/clarity) as defining features of Tretā-dharma, it implies that rulers and householders should uphold truthful speech, clean conduct, and sattvic governance to stabilize dharma in society.
No direct Vāstu or temple rule is stated; the takeaway is indirect—ritual and sacred building are ideally grounded in satya and sattva, since purity and truth are presented as supports that keep dharma “standing.”