Grande Muraglia cinese

The Great Wall (in Chinese Wanli Chángchéng), also called, in China, Great Wall of 10,000 Lǐ, is a long series of walls built in today's China from the third century BC (more precisely in 230 BC) by Emperor Qin Shi Huang, the same to whom we owe the so-called Terracotta Army of Xi'an.
Was intended to contain the raids of neighboring peoples, especially the Mongols, but proved to be very effective, because the invaders often use weaknesses represented by the door that the wall should have.
The Great Wall begins in the east at Shanhaiguan, in Hebei province, and ends at Jiayuguan, in Gansu province, to the west. Despite the Chinese name (the Lǐ is a measure that corresponds about 500 meters) the length of the wall has been, until recently, considered to be 6350 km with variable heights. In 2009, the measurements obtained with the latest technological equipment (infrared, GPS), the Great Wall would be 8851.8 km long, about 2500 km more than the 6350 estimates with the Li. The latter datum would be denied by the most recent measurements estimated at 21,196.18 km total length and 9,1 m wide of the Great Wall of China.
Before the use of bricks, the Great Wall was mainly built from rammed earth, stones, and wood. During the Ming Dynasty, however, bricks were heavily used in many areas of the wall, as were materials such as tiles, lime, and stone. The size and weight of the bricks made them easier to work with than earth and stone, so construction quickened. Additionally, bricks could bear more weight and endure better than rammed earth.
According to the records of Lin Tian the wall appears to be silver. Archaeologists explain that the wall appears to be silver because the stone they used were from Shan Xi, where many mines are found. The stone contains extremely high levels of metal in it causing it to appear silver. However, due to years of decay of the Great Wall, it is hard to see the silver part of the wall today.