From the 7th century BC to the 3rd century BC was the Spring and Autumn Period and the Warring States Period in Chinese history. During this period, countries are fiercely competing for hegemony, so the construction of military defense lines is essential for the security and stability of the country.
During the Spring and Autumn Period and the Warring States Period, the military defense line was usually dominated by the city, as the city walls could be used as fortifications to protect the city from enemy attacks. In addition, cities are also political centers and economic centers, and are one of the important pillars of the country. In order to strengthen the city's defensive capability, many cities have set up defensive facilities such as deep ditches and high fortifications, arrow towers, and beacon smoke, and regularly conduct defense drills and Xi to enhance the combat effectiveness of the army.
There is also a part of the military defense line that is a natural barrier dominated by rivers and lakes. These waters could both be used to transport supplies and personnel by ships, and they could also serve as a natural line of defense against enemy attacks. For example, the Grand Canal of the Qin Dynasty formed a strong water defense line by connecting the two major water systems of the Yellow River and the Yangtze River.
Due to the influence of the geographical environment, some mountainous areas were also used as part of the military defense line. The mountainous terrain is complex, which can be used both to conceal troops and to set traps and obstacles to hinder the enemy's advance. For example, the state of Chu took advantage of the rugged mountain roads in the south of the Yangtze River region and successfully resisted the invasion of the state of Wu.
During the Spring and Autumn Period and the Warring States Period, there were also some special cities, which were both transportation hubs and military fortresses, such as Linzi in Qi and Liang in Wei. These cities have a well-developed transportation network, which facilitates the movement and supply of soldiers, and is also an important strategic node to resist foreign invasion.
During the Spring and Autumn Period and the Warring States Period, the military defense line was a composite system composed of a variety of means, including city defense, water conservancy defense line, mountain defense, and strategic point control. Such a layout enabled the vassal states to effectively defend themselves against external threats and maintain their own security and development. With the changes of the times and the progress of technology, this traditional military defense line is also constantly evolving and developing, becoming more perfect and scientific.