Construction Material of Great Wall
Before the use of bricks, the wall was mainly built from earth, stones and wood. Due to the large quantity of materials required to construct the wall, the builders always tried to use local sources. When building over the mountain ranges, the stones of the mountain were exploited and used; while in the plains, earth was rammed into solid blocks to be used in construction. In the desert, even the sanded reeds and juniper tamarisks were used.
Before and during the Qin Dynasty (221BC-206BC), because the earth buildings could withstand the strength of weapons like swords and spears and there was low technology of productivity, the Great Wall was basically built by stamping earth between board frames. As such, only walls of plain earth or earth with gravel inside were built. No fortresses were constructed along the wall, nor bricks used in the construction of gates at the passes. Some of the walls were even made only from piles of crude stones. 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.
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Made of Bricks and Stones
Bricks were used in a lot of areas during the Ming Dynasty, as well as materials such as tiles and lime. Attempts were always made to produce the materials locally, so kiln workshops were established to burn the crude material. In a construction team there was Material Supply Department. For example, in Juyongguan Pass names of supply departments such as kiln workshops, stone ponds and material supply departments were recorded. Some materials, such as the timbers for the construction of the passes, did have to be transported from outside areas when there were none available locally.
Bricks were more a convenient material 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. According to a sample experiment experiencing gravity and erosion over a hundred years, the compressive strength, resistance to freezing and absorbency of the bricks of the time are similar to today's common bricks. A huge brick from a hundred years ago showed a high level of technological skill for that time. For further ease of construction, different shapes of brick were also burned and made to stuff into different positions.
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Stone, however, still has its advantages. Cut in rectangular shapes, they were mostly used to build the foundation, inner and outer brims, and gateways of the wall. In the Badaling section, the wall is made almost entirely of granite, some of green and white stones and some of white marble. The stone material was found to better resist efflorescence than bricks.
It is not only because of the high level of productivity of the time that hard material like bricks and stones were used in the construction, but also because of the development of weapons. Before the Ming Dynasty, the wall was built from board frames and, although not very solid, could withhold simple weapons like swords, spears and bows. But during the Ming Dynasty, gunpowder became available. The musket, blunderbuss and cannon appeared. Due to the use of these weapons, more solid bricks and stones were required to build a stronger wall.
The Great Wall of China embodies the great systems of defense created during the wars of the time; moreover it indicates a great achievement in architecture.