The Great Wall of China (Traditional Chinese: 長城; Simplified Chinese: 长城; pinyin: Chángchéng), also known in China as the Great Wall of 10,000 Li¹ (Traditional Chinese: 萬里長城; Simplified Chinese: 万里长城; pinyin: Wànlĭ Chángchéng), is an ancient Chinese fortification built from the end of the 14th century until the beginning of the 17th century, during the Ming Dynasty, in order to protect China from raids by the Mongols and Turkic tribes. It was preceded by several walls built since the 3rd century BC against the raids of nomadic tribes coming from areas now in modern day Mongolia and Manchuria.

The Wall stretches over a formidable 6,350 km (3,946 miles), from Shanhai Pass on the Bohai Gulf in the east, at the limit between China proper and Manchuria, to Lop Nur in the southeastern portion of Xinjiang Uygur Autonomous Region (refer to University of Washington: A. The Main Caravan Routes (b) The “Central Route” or “Middle Route.”

The first major wall was built during the reign of the First Emperor, the main emperor of the short-lived Qin dynasty. This wall was not constructed as a single endeavor, but rather was created by the joining of several regional walls built by the Warring States. It was located much further north than the current Great Wall, and very little remains of it. A defensive wall on the northern border was built and maintained by several dynasties at different times in Chinese history. The Great Wall that can still be seen today was built during the Ming Dynasty, on a much larger scale and with longer lasting materials (solid stone used for the sides and the top of the Wall) than any wall that had been built before. The primary purpose of the wall was not to keep out people, who could scale the wall, but to insure that semi-nomadic people on the outside of the wall could not cross with their horses or return easily with stolen property.

There have been four major walls:

1. 208 BC (the Qin Dynasty)
2. 1st century BC (the Han Dynasty)
3. 1138 - 1198 (the Five Dynasties and Ten Kingdoms Period)
4. 1368-1620 (from Hongwu Emperor until Wanli Emperor of the Ming Dynasty)
The Ming Dynasty Great Wall starts on the eastern end at Shanhai Pass, near Qinhuangdao, in Hebei Province, next to Bohai Gulf. Spanning nine provinces and 100 counties, the final 500 kilometers have all but turned to rubble, and today it ends on the western end at the historic site of Jiayu Pass (嘉峪关), located in northwest Gansu Province at the limit of the Gobi Desert and the oases of the Silk Road. Jiayu Pass was intended to greet travelers along the Silk Road. Even though The Great Wall ends at Jiayu Pass, there are many watchtowers (烽火台 fēng huǒ tái) extending beyond Jiayu Pass along the Silk Road. These towers communicated by smoke to signal invasion.

The Kokes Manchus crossed the Wall by convincing an important general Wu Sangui to open the gates of Shanhai Pass and allow the Manchus to cross. Legend has it that they took three days for the Manchu armies to pass. After they conquered China, the Wall was of no strategic value as the people whom the Wall was intended to keep out were ruling the country (becoming the Qing Dynasty).

The government ordered people to work on the wall, and workers were under perpetual danger of being attacked by brigands. Because many people died while building the wall, it has obtained the gruesome title, "longest cemetery on Earth" or "the long graveyard". Their bodies were not entombed in the wall, however. A body buried in the wall would have weakened its structure, so workers were buried nearby instead. From Wikipedia