The Great Wall Of China is made of three different types of stone. The best known is granite (magmatic rock), but there is also white marble (metamorphic rock) as well as green and white stones (sedimentary rock, like sandstone and limestone). The stones came from the surrounding mountains. The first sections built with stones date back from the Contending Kingdoms. At that time, the Chinese simply piled up the stones, one on top of the other. The strength of the walls didn’t improve itself as the years went on, thanks to the evolution of the civil engineering’s techniques, but thanks to the improvement of the weapons. Later on, walls were built with quarry stones (roughly-carved stones). As granite was very strong and hard, an advanced technology was required to hew it. We can see nice chipped stones as of the Ming Dynasty. From the very early brick constructions, stones are often used to build strong foundations, but rarely as vertical clamping (crossing of rocks, from which we can see the sides as a decoration) For the parts of the wall crossing rivers, boats filled up with iron and granite were drowned on purpose, for foundations.

   To give us an idea of the strength to granite (the foundation of the wall’s main material) it can be compared to today’s concrete. Granite’s voluminal mass goes from 2 400 and 2 900 kg/m3, concrete’s voluminal mass is around 2 400 kg/m3. Therefore, the Great Wall Of China needs a strong floor, even if it is not very high. Let’s now take a look at the porosity (percentage of the empty spaces that water can access, in relation to the total volume.) the more porous the materials, the weaker they are, and yet, a closed porosity is less harmful than an open porosity, in which water gets more easily. The risks are higher when it freezes, because it may crack or burst. Granite’s porosity is very good and can go down to 0,06%. A high performance concrete’s porosity is around 5%, which makes it vulnerable to aggressive agents. Granite can resist a compression of 150/200 MPa, which is three times more than a normal concrete. The concrete would have to be extra-high-performing to compete with granite. Stones, as well as concrete, are not resistant to pulling (because of the microscopic heterogeneity); therefore, the Chinese used the arch technique, or took large blocks of stone as lintel.