The ninth chapter is the Art of War's most operationally detailed section, providing practical guidance for managing troops in different environments — mountain terrain, river crossings, salt marshes, and level ground. More significantly for martial arts practitioners, it teaches the art of reading signs: interpreting the opponent's condition through careful observation of subtle indicators.

The title 行军 (Xíngjūn) combines 行 (Xíng, to march or move) with 军 (Jūn, army). The chapter concerns the practical management of forces in motion.

Reading the Enemy

The chapter's most valuable section for martial application catalogues dozens of observational indicators. When dust rises sharply, chariots are coming. When dust is low and broad, infantry is advancing. When birds suddenly take flight, an ambush is prepared. When animals are startled, a surprise attack approaches.

Sūnzǐ extends this to reading the enemy's condition through his behavior: envoys who speak humbly while preparations increase are planning an advance. Those who speak aggressively while appearing to retreat are preparing to withdraw. When troops lean on their weapons, they are hungry. When water-carriers drink before delivering, the army thirsts.

In Wudang combat, this art of reading translates to observing the opponent's body language: the shift of weight that precedes a step, the tension in the shoulder that announces a strike, the breath pattern that reveals fatigue or preparation, the eye movement that betrays intention. Tīngjìn (听劲, listening energy) is not only tactile — it is also visual. The skilled practitioner reads the opponent's condition before contact is made.

Terrain Management

The chapter provides specific guidance for four types of terrain: mountains (camp on high ground with the sun at your back), rivers (do not engage near water — let the enemy cross halfway before striking), marshes (cross quickly, never linger), and level ground (position with rising ground to your rear). These operational details, while military in context, illustrate the broader principle that the environment is not neutral — it can be used as advantage or allowed to become disadvantage.