壘虛

King Wu asked Taigong: "How can one know whether the enemy's ramparts are occupied or empty, and whether they are coming or going?" Taigong said: "A general must understand the patterns of heaven above, the principles of terrain below, and human affairs in between. Climb to a height and look down to observe the enemy's movements. By observing their ramparts, you can know whether they are full or empty. By observing their soldiers, you can know whether they are advancing or withdrawing."

King Wu said: "How can one know these things?" Taigong said: "Listen — if their drums make no sound and their bells produce no noise; observe — if many birds alight on their ramparts without being startled and there is no dust or haze above them — you may be certain the enemy is using decoys in the form of straw dummies. If the enemy has just departed but has not gone far, and they turn back before settling — this means they are driving their soldiers too hard. When driven too hard, front and rear lose cohesion; when cohesion is lost, their formations must be in disorder. In such circumstances, rush out troops to strike them. Even with few attacking many, you will certainly prevail."