The Great Wall of China

The Great Wall of China is a series of fortifications of stone, brick, rammed earth, wood, and other materials, usually built along a line from east to west through the historic northern borders of China, partly to protect the Chinese Empire or intrusion prototypical states of various nomadic groups or military incursions by various peoples or military forces. Several walls were already built in the seventh century BC; these later joined and made bigger and stronger, now collectively referred to as the Great Wall. Especially famous is the wall built between 220-206 BC by the first Emperor of China, Qin Shi Huang. Little of that wall remains. Since then, the Great Wall and off has been reconstructed, maintained and improved; the majority of the existing wall is of the Ming dynasty. 

Other effects of the Great Wall have included border controls, which allows the imposition of taxes on goods transported along the Silk Road, the regulation or the promotion of trade and control of immigration and emigration . Moreover, the defensive characteristics of the Great Wall were enhanced by the construction of watchtowers, barracks for troops, stations garrison, signaling capabilities by means of smoke or fire, and the fact that the road Great Wall also served as a transportation corridor. 

The main line of the Great Wall stretches from Shanhaiguan in the east, to Lop Lake in the west, along an arc that roughly delineates the southern edge of Inner Mongolia. A comprehensive archaeological survey, using advanced technologies, has concluded that the Ming walls measured 8,850 kilometers (5,500 mi). This consists of 6259 kilometers (3889 miles) sections of actual wall, 359 km (223 mi) of trenches and 2,232 km (1,387 miles) of natural defensive barriers such as hills and rivers. Another archaeological study found that entire wall with all its branches to be measuring 21,196 kilometers (13,171 miles). 

The first walls: 

The Chinese were already familiar with the techniques of wall-building era of the Spring and Autumn period between the eighth and fifth centuries BC.  During this time period and the subsequent Warring states of Qin, Wei, Zhao, Qi, Yan and Zhongshan  all constructed extensive fortifications to defend their own borders. Built to withstand the attack of small, such as swords and spears, these walls were made weapons mostly by stamping earth and gravel between board frames. 

Qin Shi Huang conquered all opposing states and unified China in 221 BC, establishing the Qin Dynasty. With the intention to impose a centralized government and prevent the resurgence of feudal lords, he ordered the destruction of the wall sections that divided his empire along the former state borders. To position the empire against the Xiongnu people from the north, he ordered the construction of new walls to connect the remaining fortifications along the northern border of the empire. Transporting the large quantity of materials required for construction was difficult, so builders always tried to use local resources. Stones from the mountains were used in mountain ranges, while rammed earth was used for construction in the plains. There are no surviving historical records indicating the exact length and course of the Qin Dynasty walls. Most of the ancient walls have eroded over the centuries, and very few sections remain today. The human cost of construction is unknown but has been estimated by some authors that hundreds of thousands, if not up to a million, workers died building the Qin wall. Later, the Han, Sui, and Northern dynasties all repaired, rebuilt, or sections of the Great Wall were expanded at great cost to defend themselves against northern invaders. The Tang and Song Dynasties did not build the walls in the region substantially. The Liao, Jin and Yuan dynasties that ruled northern China in most of the 10-13th centuries, walls built in the 12th century but which are much farther north of the Great Wall as we know, in inner and Outer Mongolia today.