Introduction to the Ninth Chapter: The Ninth "March Chapter" discusses how to position the army and judge the enemy's situation during marching operations. It also discusses the differences between the army in four types of terrain: mountains, rivers, salt-alkali swamps, and plains. It also discusses how to deal with special terrain such as Jujian, Tianjing, Tianlao, Tianluo, Tianzhen, Tiangai, etc. Sun Wu also proposed 31 methods of observing and judging the enemy's situation. Through these methods, we can analyze various phenomena seen, heard and detected, and grasp the real enemy situation, so that we can formulate correct combat plans and win victory. In this article, Sun Wu also put forward the principle of military management using both civil and military forces to "order with words and coordinate with force", that is, we must use morality to educate soldiers and use laws and disciplines to unify the pace. Such an army will definitely be able to fight. Achieve victory.