द्वयोरट्टालकयोर्मध्ये सहर्म्यद्वितलामध्यर्धायायामां प्रतोलीं कारयेत् ॥ कZ_०२.३.११ ॥
dvayor aṭṭālakayor madhye saharmyadvitalāmadhyardhāyāyāmāṃ pratolīṃ kārayet
Between two watchtowers he should build a gatehouse (pratolī), integrated with an upper structure (with rooms), of two storeys, and of the prescribed intermediate/half-length dimensions.
It allows cross-coverage of the gate by defenders from both sides, turning entry into a controllable and punishable chokepoint.