The Army on the March

This chapter is a field manual in two halves: where to place an army in different country, and how to read the enemy from the signs he gives off. On crossing mountains, keep to the valleys and camp on high ground facing the sun — never climb to attack an enemy on the heights. After crossing a river, get far from it; let an invader cross before you strike, attacking him mid-passage when half his force is over. In salt marshes, get across quickly and camp near grass and water with trees at your back. On level ground take an accessible position with rising ground to your right and rear, "so that the danger may be in front, and safety lie behind." Each terrain dictates its own discipline, and these four classic placements are how, Sun Tzu notes, the Yellow Emperor vanquished four rivals.

He prefers high, sunny, dry ground for the army's health and footing, and warns against low, damp positions where disease breeds. Where there are steep banks, ponds, reeds, or dense scrub near the camp, search them carefully — "for these are places where ambushes are likely to lurk."

The chapter's celebrated passage is the reading of signs. When the enemy is close and quiet, he relies on a natural strength; when he tries to provoke from far off, he wants you to advance. Trees moving signals the enemy advancing; many screens of grass means he is trying to mislead you; birds rising in flight reveal an ambush; startled beasts reveal a sudden attack. High, sharply-peaked dust means chariots; low, wide dust means infantry; scattered, thin dust means men gathering firewood. Humble words with increased preparations mean an advance is coming; violent language and a feigned charge mean retreat. When soldiers lean on their spears they are faint with hunger; when those who draw water drink first they are parched; when the enemy sees an advantage and does not take it, he is exhausted.

On the human side, Sun Tzu balances discipline with humanity. Numbers alone give no advantage; do not advance on mere brute strength. Concentrate force, read the enemy, and gain men — that is enough. He who "exercises no forethought but makes light of his opponents is sure to be captured."

His final principle is the foundation of cohesion: soldiers must be treated with humanity but kept under control by iron discipline — "this is a certain road to victory." If a general punishes troops before they have grown attached to him, they will not be submissive; if he fails to punish after attachment is formed, they remain useless. So command them with courtesy and weld them together with discipline. If orders are habitually enforced, the army is well-disciplined; if not, it is not. The lesson endures for any leader: position determines health and safety; small signals reveal the true state of a rival; and authority works only when warmth and consistent enforcement go together.