पृथुशिलासंहतं वा शैलं कारयेत् न त्वेव काष्टमयम् ॥ कZ_०२.३.०८ ॥
pṛthuśilāsaṃhataṃ vā śailaṃ kārayet na tveva kāṣṭamayam
He should have it built of rock—either of broad stone slabs tightly bonded or of solid stone; but not made of timber.
Timber increases vulnerability to fire, decay, and enemy sabotage; stone improves survivability under siege and reduces maintenance risk.