In total, three million square meters will have been used for the construction of the Great Wall. The parts built under the Contending Kingdoms are mainly made of earth, rammed earth or clay and straw mortar. The mixture of clay and straw was held together thanks to the straw, which made it stronger and improved the cohesion. In certain areas, particularly in the Golbi Desert, (during the Han’s time) straw was replaced by reeds. The rammed earth was made of clayed earth and of pebbles packed in casings, with the help of feet. They used a mixture of 15% of clay and 60% of sand, the rest being stones and lime. They tamped the earth in layers of approximately fifteen centimetres, the wall built in concrete, using shelters, and being fifty centimetres wide. The Great wall was then a stratified wall. The compressive strength could rise up to 5MPa or even more with a hydraulic binding agent. The earth used on its own, without straw, couldn’t be too damp. Therefore, it was extracted from the soil in spring. The ratio of the constituents of rammed earth, its origin and its chemical nature depend on the territory, from ochre brown, to light brown.

   The Chinese didn’t care much about the excellent temperature lag and the very good soundproofing of the earth; what interested them was the real advantage of this material: its proximity and its availability. Indeed, only the Zhao and the Han may have had problems with these resources as the Golbi Desert was closer. For any earth-building, a lot of hand work is required, particularly at that time. But what remains the building’s weakest point is its vulnerability to rain, especially at its base.