Why Can Ancient City Walls Stand for Thousands of Years?

Many people are shocked by the weathered city walls when visiting ancient cities, but few know that these buildings, which have withstood thousands of years of wind and rain, contain the architectural wisdom of the ancients. Taking the Xi’an Ming City Wall and Pingyao Ancient City Wall as examples, the reason they can stand for hundreds or even thousands of years lies in three core architectural techniques. First, material selection: the ancients mostly used local loess, blue bricks, and glutinous rice mortar as an adhesive—glutinous rice mortar, made by mixing glutinous rice, lime, and sand, has extremely strong viscosity, comparable to modern cement, and is waterproof and corrosion-resistant, effectively resisting wind and rain erosion. Second, structural design: the city walls adopt a “trapezoidal structure”, with a wider bottom and a narrower top, lowering the center of gravity to enhance overall stability. At the same time, horse faces (defensive platforms protruding from the city walls) are installed on the wall surface, which not only facilitates defense but also disperses the force on the wall. Finally, the drainage system: drainage ditches are installed on the top of the city walls, and drip eaves are installed on the wall surface, which can quickly drain rainwater and avoid rainwater seeping into the wall and causing collapse. In addition, the ancients would regularly maintain the city walls, using methods such as “brick patching and grouting” to keep them intact. When visiting ancient city walls, you may wish to pay attention to the brick patterns and the design of horse faces. Every detail is a crystallization of the ancients’ wisdom. Understanding these popular science knowledge can make your trip to the ancient city more meaningful and help us better inherit and protect these precious cultural heritage.