that the enemy may throw poison on the water to be carried down to us. Capt. Calthrop’s first version was: “Do not cross rivers in the face of the stream” — a sapient piece of advice, which made one curious to know what the correct way of crossing rivers might be. He has now improved this into: “Do not fight when the enemy is between the army and the source of the river.”
So much for river warfare.
7. In crossing salt-marshes, your sole concern should be to get over them quickly, without any delay.
Because of the lack of fresh water, the poor quality of the herbage, and last but not least, because they are low, flat, and exposed to attack.
8. If forced to fight in a salt-marsh, you should have water and grass near you, and get your back to a clump of trees.
Li Ch‘üan remarks that the ground is less likely to be treacherous where there are trees, while Tu Yu says that they will serve to protect the rear. Capt. Calthrop, with a perfect genius for going wrong, says “in the neighbourhood of a marsh.” For 若 the T‘ung Tien and Yü Lan wrongly read 爲, and the latter also has 倍 instead of 背.
So much for operations in salt-marshes.
9. In dry, level country, take up an easily accessible position
This is doubtless the force of 易, its opposite being 險. Thus, Tu Mu explains it as 坦易平穩之處 “ground that is smooth and firm,” and therefore adapted for cavalry; Chang Yü as 坦易無坎陷之處 “level ground, free from depressions and hollows.” He adds later on that although Sun Tzŭ is discussing flat country, there will nevertheless be slight elevations and hillocks.
with rising ground to your right and on your rear,