The Great Wall of China is a series of fortifications made of stone, brick, tamped earth, wood, and other materials, generally built along an east-to-west line across the historical northern borders of China to protect the Chinese states and empires against the raids and invasions of the various nomadic groups of the Eurasian Steppe. Several walls were being built as early as the 7th century BC; these, later joined together and made bigger and stronger, are now collectively referred to as the Great Wall. Especially famous is the wall built 220 206 BC by Qin Shi Huang, the first Emperor of China. Little of that wall remains. Since then, the Great Wall has on and off been rebuilt, maintained, and enhanced; the majority of the existing wall is from the Ming Dynasty (1368 1644).
Other purposes of the Great Wall have included border controls, allowing the imposition of duties on goods transported along the Silk Road, regulation or encouragement of trade and the control of immigration and emigration. Furthermore, the defensive characteristics of the Great Wall were enhanced by the construction of watch towers, troop barracks, garrison stations, signalling capabilities through the means of smoke or fire, and the fact that the path of the Great Wall also served as a transportation corridor.
The Great Wall stretches from Dandong 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 measure 8,850 km (5,500 mi). This is made up of 6,259 km (3,889 mi) sections of actual wall, 359 km (223 mi) of trenches and 2,232 km (1,387 mi) of natural defensive barriers such as hills and rivers. Another archaeological survey found that the entire wall with all of its branches measure out to be 21,196 km (13,171 mi).
The collection of fortifications now known as “The Great Wall of China” has historically had a number of different names in both Chinese and English.
The Great Wall of China built during the Ming dynasty begins near Jiayu Pass and ends in Shanhai Pass in Korea Bay. The Ming Great Wall is generally considered the main line of the Great Wall of China, though walls from other periods of Chinese history are also included in the Great Wall. The total length of walls built by all dynasties is approximately 13,100 miles. Other dynasties, including Han, Northern Wei, Northern Qi and Jin, contributed extensive wall fortifications. These walls are scattered throughout China with multiple start and end points.