Moat introduction: The moat is the ditch surrounding the city. In order to defend against invasion by foreign enemies, ancient humans dug trenches around settlements, and the resulting belt-like highlands inspired people to build walls. The emergence of the city can be seen as the result of taking soil from the site when the city wall was first built. The accumulated water in Hao Nei formed a pond and a river, which became an insurmountable line of defense. "Only the city surrounds the people, but the pond surrounds the city." The "pool" is the barrier of the "city", so it is often called "moat". The suspension bridge is a wooden plank bridge spanning the city moat. The outward end of the bridge is tied with a rope. The bridge deck can be lifted at any time through pulleys and winches to cut off the incoming and outgoing routes.