The Great Wall is not a single structure but the sum of defensive lines built over centuries by different dynasties, in different materials and techniques. Architecturally its most instructive feature is the technique used in its oldest and longest sections: hangtu — rammed earth.

In hangtu, two parallel timber forms are set up; moist earth (sometimes mixed with lime, gravel, or straw) is poured between them in thin layers, and each layer is pounded with heavy rammers until it reaches almost the hardness of stone. When the form is full it is lifted, and the process repeats; the wall rises in horizontal strata. The result is a solid, inward-battered rampart requiring no mortar or firing, built from local earth and labour alone. In the Qin and Han periods, hundreds of kilometres were raised this way across desert and steppe; the dry climate let these earthen walls survive two thousand years.

Later, especially under the Ming, the wall was faced with stone and fired brick and took the tall, crenellated form recognised today. But the structural lesson is in the early sections: a vernacular technique adapted to the terrain, demanding no special material, gaining durability through compaction alone. The Great Wall thus shows that earth too — as much as stone and brick — can be a monumental and lasting building material.