The defensive construction of the Great Wall has accumulated rich experience over the course of more than two thousand years of construction.
Firstly, in terms of layout, the important principle of "adapting to the terrain, utilizing strategic points" was summarized during the construction of the Great Wall by Qin Shi Huang, and it was later recorded in the "Records of the Grand Historian" by Sima Qian. This principle was followed by subsequent dynasties in the construction of the Great Wall, becoming an important basis for military defense. All the passes were built between mountains and valleys, at bends in rivers, or at strategic locations on plains to control important passages. This approach not only allowed for better control of strategic points but also saved manpower and resources, achieving the desired effect of "one man can hold the pass against ten thousand enemies." Castles and beacon towers were also built at strategic locations. As for the construction of the wall itself, the topography was fully utilized. For example, the Great Wall sections at Juyong Pass and Badaling in Beijing were built along the ridges of mountains, appearing steep from the outside but relatively gentle on the inside, thus achieving the effect of "easy to defend, difficult to attack." In Liaoning Province, there is a type of Great Wall known as "Shanxian Wall" or "Pishan Wall," which is constructed by steep cliffs, forming a part of the Great Wall. In some areas, natural barriers such as cliffs, rivers, and lakes were fully utilized as natural barriers.
The construction of the Great Wall employed the principle of "utilizing local materials and adapting construction methods accordingly," resulting in the creation of various structural techniques. These included structures made of rammed earth, stone blocks, stone slabs, and a combination of bricks and stones. In desert areas, structures were built using layers of red willow branches, reeds, and sand. Examples of these ancient structures can still be found in places such as Yumen Pass and Yang Pass in Gansu Province, as well as in Xinjiang, dating back over two thousand years to the Western Han Dynasty.
With the progress of social productivity, brick-making technology continued to develop, and during the Ming Dynasty, brick production increased significantly. Bricks were no longer considered precious building materials, which led to the use of large bricks in the construction of many sections of the Ming Great Wall, both on the inner and outer peripteral walls of the city walls. Despite relying solely on manual construction and transportation of building materials, using bricks of relatively small weight and uniform size for wall construction not only facilitated construction but also increased construction efficiency and improved the overall level of architecture. Additionally, many gateways at the passes were constructed with large-span arches made of blue bricks. Although some of these blue bricks have weathered significantly, the gateways still stand majestically, showcasing the exceptional skill in arch construction at that time. Looking at the architectural decorations on the towers of the passes, many intricately carved stone and brick sculptures demonstrate the complex and delicate production techniques, reflecting the artistic talent and craftsmanship of the artisans of that time.
