Matsya Purana — Measures of Time: Caturyuga Computation
चत्वारि भारते वर्षे युगानि ऋषयो ऽब्रुवन् कृतं त्रेता द्वापरं च कलिश्चैवं चतुर्युगम् //
catvāri bhārate varṣe yugāni ṛṣayo 'bruvan kṛtaṃ tretā dvāparaṃ ca kaliścaivaṃ caturyugam //
In Bharata-varṣa, the seers declared that there are four ages—Kṛta (Satya), Tretā, Dvāpara, and Kali—thus constituting the fourfold cycle called caturyuga.
This verse does not describe Pralaya directly; it defines the temporal framework (caturyuga) within which creation, preservation, decline of dharma, and periodic dissolutions are understood in Purāṇic cosmology.
By naming the four yugas, it signals that dharma and social duties are taught with awareness of changing times—kings and householders are expected to uphold order appropriate to their age, especially as righteousness diminishes toward Kali.
No direct Vāstu or ritual rule appears here; its practical significance is contextual—temple rites, donations, and disciplines are often prescribed differently by yuga in Purāṇic literature, and this verse establishes that yuga-based framework.