Kautilya's Arthashastra 13.4.9

13.4.9

kṛtvā skandhāvārasya rakṣāṃ vīvadhāsārayoḥ pathaś ca, parikṣipya durgaṃ khātasālābhyām, dūṣayitvodakam, avasrāvya parikhāḥ sampūrayitvā vā, suruṅgābalakuṭikābhyāṃ vapraprākārau hārayet, dāraṃ ca guḍena //

Having well guarded his camp, transports, supplies and also the roads of communication, and having dug up a ditch and raised a rampart round his camp, he may vitiate the water in the ditches round the enemy's fort, or empty the ditches of their water or fill them with water if empty, and then he may assail the rampart and the parapets by making use of underground tunnels and iron rods. If the ditch (dváram) is very deep, he may fill it up with soil. If it is defended by a number of men, he may destroy it by means of machines. Horse soldiers may force their passage through the gate into the fort and smite the enemy. Now and then in the midst of tumult, he may offer terms to the enemy by taking recourse to one, two, three, or all of the strategic means.