Matsya Purana — The Cave-Sanctuary: Jewel-Lake
प्रमाणेन तथा सा च द्वे च राजन्धनुःशते चतुरस्रा तथा रम्या तपसा निर्मितात्रिणा //
pramāṇena tathā sā ca dve ca rājandhanuḥśate caturasrā tathā ramyā tapasā nirmitātriṇā //
By proper measure, O King, it should extend to two hundred dhanus; it is to be square in plan, pleasing in appearance, and fashioned with disciplined tapas, using grass as the laying or marking material.
This verse is not about Pralaya; it belongs to the Vastuvidya stream of the Matsya Purana and focuses on measured construction and orderly planning rather than cosmic dissolution.
It frames town/settlement planning as a royal responsibility: the king is advised to establish habitations by fixed standards (pramāṇa), emphasizing governance through orderly, proportionate, and aesthetically auspicious civic design.
Architecturally, it prescribes a square plan and a defined extent (two hundred dhanus). The mention of tṛṇa (grass) plausibly points to traditional site-marking/laying-out practice, where grass cords or grass lines help demarcate measurements during planning.