Matsya Purana — Measures of Time: Caturyuga Computation
एषा द्वादशसाहस्री युगसंख्या तु संज्ञिता कृतं त्रेता द्वापरं च कलिश्चेति चतुष्टयम् //
eṣā dvādaśasāhasrī yugasaṃkhyā tu saṃjñitā kṛtaṃ tretā dvāparaṃ ca kaliśceti catuṣṭayam //
This is known as the yuga-count of twelve thousand (years): the fourfold set consisting of Kṛta, Tretā, Dvāpara, and Kali.
It defines the fundamental time-unit (the four yugas as a 12,000-year measure), which is used in the Matsya Purana to compute larger cycles that culminate in periodic dissolutions (pralayas).
By naming the four yugas, it implies that dharma and social duties vary with time; rulers and householders are expected to align conduct with the yuga’s prevailing strength of dharma, a recurring ethical theme in the Matsya Purana.
No direct Vāstu or ritual rule is stated; however, yuga-chronology often frames when particular rites, temple practices, and standards are said to flourish or decline across ages in Purāṇic discussions.