Kautilya's Arthashastra 10.2.18

10.2.18

ekāyanamārgaprayātasya senāniścāragrāsāhāraśayyāprastārāgninidhāna.dhvajāyudhasaṃkhyānena parabalajñānam //

When the enemy's army is marching through a path traversable by a single man, the commander (of the invader's army) should ascertain its strength by estimating the quantity of food-stuffs, grass, bedding, and other requisites, fire pots (agninidhána), flags and weapons. He should also conceal those of his own army.