Matsya Purana — Solar–Lunar Motions
प्रमाणं मण्डलस्यापि योजनानां निबोधत योजनानां सहस्राणि दश चाष्टौ तथा स्मृतम् //
pramāṇaṃ maṇḍalasyāpi yojanānāṃ nibodhata yojanānāṃ sahasrāṇi daśa cāṣṭau tathā smṛtam //
Now understand the measure of the maṇḍala in yojanas: it is traditionally remembered as eighteen thousand yojanas.
It does not directly describe pralaya; it gives a cosmological-scale standard for a maṇḍala’s measurement, reflecting the Purāṇic habit of linking sacred geometry with cosmic dimensions.
By prescribing authoritative measurements, it supports dharmic governance and household/royal building activity—ensuring settlements, ritual spaces, and constructions follow recognized Vāstu standards rather than arbitrary design.
The verse states the maṇḍala’s pramāṇa as 18,000 yojanas, indicating a canonical dimension for the mandala concept used in Vāstu planning and ritual spatial layout (a cosmic template mirrored in architecture).