The building concept of border defence facilities of Qin: Watchtowers along the King of Zhaoxiang great wall in Shaanxi province

Qin was a military power during the Warring States period, and in its confrontations with other regimes, it constructed a series of border defense projects, among which the most iconic is the Great Wall. Watchtowers are an important part of the Great Wall defense system, and their function was to provide soldiers with a better vantage point and shooting position. This paper studies the 347 watchtowers along the King of ZhaoXiang Great Wall (ZXGW) in Shaanxi Province, categorizes their architectural forms, and determines the distribution characteristics, and aims to understand the construction philosophy of the Qin state's border defense projects through the early prototypes of watchtowers. These watchtowers were built by earth on-site, and likely with subsidiary buildings. Relevant literature and analysis on ArcGIS show different distribution characteristics and defense capability across the different geographical environments in the east, middle, and west sections. The watchtowers of the western section, situated in the Baiyu mountainous area, are taller and most densely distributed, thus offering the most significant defensive advantage of the three sections. The watchtowers in the eastern section, located in a relatively flat and hilly area with the lowest heights and distributed sparsely, provide the weakest defensive capability. The middle section serves as a transition zone between the east and west sections, with the height, distribution density, and defense advantages of watchtowers occupying a similar middle-ground position.