What is the Great Wall of China made of?

The construction materials of Great Wall of China mainly are earth, wood, stones, sand, and bricks, in different construction time and different construction sites with different climates and local materials.

Due to the large quantity of materials required to construct the wall, the builders usually obtained materials from local sources. When building over the mountain ranges, the stones of the mountain were exploited and used, while in the plains, earth rammed into solid blocks was used in construction. In the desert, even the branches of reeds and red willows were paved with sand by turns. In addition, the wooden planks were used as the flank wall in some sections. With the development of brick-making techniques, the bricks were used in the construction since Tang Dynasty (618 – 907 AD).
Great Wall constructed with  sand and earth
Great Wall Constructed with Sand and Earth
Mutianyu Great Wall made of  bricks and stones
Great Wall Made of Bricks and Stones

Earth, Woods, Branches, Sand and Stones
– Construction Materials of Great Wall before Sui (7 Cen. BC – 618 AD)

Due to the earthen buildings could withstand the strength of cold weapons like swords and spears, as well as the low technology of productivity before the Sui Dynasty (518 – 618 AD), the most Great Wall sections were built by ramming earth between board frames. Some of the walls were rammed with earth, lime, sand and small stones. In the desert, some walls were rammed with the branches of reeds and red willows and sand layer-by-layer. Around Dunhuang City in Gansu Province, Yulin City in Shaanxi Province and Baotou City in Inner Mongolia, sites can still be found from the Great Wall of Qin, Han and Zhao. The Wall of Zhao was built during the Warring States Period using board frames, and the layers of earth can still be clearly seen.

Besides, some sections were built with the sun-dried mud brick, which covered by the yellow clay as the protection. This kind of the sections were usually built in the areas with the dry climate and rare rain. The Jiayuguan Pass in Gansu Province is a representative one.
 

Earth, Bricks and Stones
– Construction Materials of Great Wall during Tang and Song (618 – 1279 AD)

The brick-making techniques developed a lot during Tang and Song Dynasties. However, the bricks were quite valuable at that time, which could not be widely used in the construction. Therefore, the laboring people started to build the passes and the wall around the passes with the bricks wrapped outside and the yellow mud filled inside. Some places also used the stones to build the wall during that period. This kind of the Great Wall was much firmer than the wall built with sun-dried mud brick or rammed earth.  
Great Wall Stone
Stone Used in Building the Great Wall
Great Wall Brick with Flower Patterns
Great Wall Brick with Flower Patterns

Bricks and Stones
– Construction Materials of Great Wall of Ming (1368 – 1644 AD)

Till the Ming Dynasty (1368 – 1644 AD), the brick-making techniques made a great progress that both quantity and quality of production were improved a lot. Since then, the Great Wall sections had been widely laid with bricks, moreover, the lime mortar and sticky rice were used to reinforce the bricks. The wall in this period could not only resist the invasions of nomadic tribes, but also could protect the terrain and people from cold weapons and some firearms.

In addition, some walls were built along the mountains where there were plenty of stones available. Therefore, the workers used the locally available stones to build the wall. The stone walls were quite firm to defense against enemies and withstand the natural erosion. There is a wall near Badaling section, which is made of the huge stones, and put lime mortar and sticky rice in crevices to reinforce the wall.

Stone, cut in rectangular shapes were mostly used to build the foundation, inner and outer brims, and gateways of the wall. Bricks were more advanced materials than earth and stone as their small size and light weight made them convenient to carry and thus quickened the speed of construction. Bricks are also the ideal material to bear the weight. Therefore, the bricks were used as the upper layers of the walls to resist the attacks from various weapons. For further ease of construction, different shapes of brick were also burned and made to stuff into different positions.
 

How many bricks were used to construct the Great Wall?

There might to be approximately 3,873,000,000 individual bricks used to build the Great Wall of China, though the precise number remains unresolved. Generally speaking, the most bricks of the wall measure 0.37 meters (1.2 feet) long, 0.15 meters (0.5 feet) wide and 0.09 meters (0.3 feet) thick. Here is a rough estimate that if all the bricks are connected, the total length of the bricks can loop around 36 rounds of the equator.