9. The Army on the March
See supra, ss. 2. The repetition of these words in connection with water is very awkward. Chang Yu has the note: "Said either of troops marshaled on the river-bank, or of boats anchored in the stream itself; in either case it is essential to be higher than the enemy and facing the sun." The other commentators are not at all explicit.
Tu Mu says: "As water flows downwards, we must not pitch our camp on the lower reaches of a river, for fear the enemy should open the sluices and sweep us away in a flood. Chu-ko Wu-hou has remarked that 'in river warfare we must not advance against the stream,' which is as much as to say that our fleet must not be anchored below that of the enemy, for then they would be able to take advantage of the current and make short work of us." There is also the danger, noted by other commentators, that the enemy may throw poison on the water to be carried down to us.
So much for river warfare.