Kautilya's Arthashastra 10.2.16

10.2.16

anudake cakricatuṣpadaṃ cādhvapramāṇena śaktyodakaṃ vāhayet //

He should protect his army when it has to pass a long desert without water; when it is without grass, firewood and water; when it has to traverse a difficult road; when it is harassed by an enemy's attacks; when it is suffering from hunger and thirst after a journey; when it is ascending or descending a mountainous country full of mire, water-pools, rivers and cataracts; when it finds itself crowded in a narrow and difficult path; when it is halting, starting or eating; when it is tired from a long march; when it is sleepy; when it is suffering from a disease, pestilence or famine; when a great portion of its infantry, cavalry and elephants is diseased; when it is not sufficiently strong; or when it is under troubles. He should destroy the enemy's army under such circumstances.