First, wars often occurred in ancient times, so the ancients built moats with defensive functions. This greatly increases the city's defense, and the moat can effectively slow down the enemy's attack and play a role in isolation and buffering. Without a moat, the enemy can line up to charge when attacking. The moat needs to be filled or bridged, and the enemy can only go up in the form of buffer. In this way, an attack from the surface becomes a point attack, and the defenders in the city only need to concentrate on defending a few breakthrough points, so it is difficult for the enemy to attack the city.
Second, the moat also has a self-help function. It can not only prevent the enemy's fire attack, but also meet the needs of urban water use. It is also an important water conservancy project for flood control and drainage, and some of them can also undertake transportation functions near rivers.
Third, the mud dug in the moat can also be used to burn bricks and build city walls. In this way, the freight is also saved, which greatly saves the cost of building the city wall.
Let's take a look at the moat of Xiangyang city again. Xiangyang moat is wide and there are many objective factors. The historical position of Beijing, Xi, Luoyang and Nanjing is more important than that of Xiangyang, but due to the limitation of natural conditions, their moats are not as wide as Xiangyang.
Xiangyang moat was not so wide at the beginning of its construction, but it has experienced the process of widening and deepening. Whenever there is a war, residents in the city can drink water directly from the moat.