Kautilya's Arthashastra 2.3.4

2.3.4

tasya parikhās tisro daṇḍāntarāḥ kārayet caturdaśa dvādaśa daśeti daṇḍān vistīrṇāḥ, vistārād avagāḍhāḥ pādonam ardhaṃ vā, tribhāgamūlāḥ, mūlacaturaśrā vā, pāṣāṇopahitāḥ pāṣāṇeṣṭakābaddhapārśvā vā, toyāntikīr āgantutoyapūrṇā vā saparivāhāḥ padmagrāhavatīś ca //

Round this fort, three ditches with an intermediate space of one danda (6 ft.) from each other, fourteen, twelve and ten dandas respectively in width, with depth less by one quarter or by one-half of their width, square at their bottom and one-third as wide as at their top, with sides built of stones or bricks, filled with perennial flowing water or with water drawn from some other source, and possessing crocodiles and lotus plants shall be constructed.