Building the Great Wall
After the Ming army defeat at Battle of Tumubao and later raids by the Mongols under a new leader, Altan Khan, the Ming adopted a new strategy for dealing with the northern horsemen： a giant impregnable wall.
Almost 100 years earlier (1368) the Ming had started building a new, technically advanced fortification which today is called the Great Wall of China.
Created at great expense the wall followed the new borders of the Ming Empire.
Acknowledging the control which the Mongols established in the Ordos, south of the Huang He, the wall follows what is now the northern border of Shanxi and Shaanxi provinces.
Work on the wall largely superseded military expeditions against the Mongols for the last 80 years of the Ming dynasty and continued up until 1644, when the dynasty collapsed.
The Great Wall seen today was built during the Ming Dynasty (明朝）， on a much larger scale and with longer lasting materials than any wall built before.
The primary purpose of the wall was not to keep out people, who could climb the wall, but make it difficult for semi-nomadic people outside the wall to cross with their horses or return with stolen property.
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 (丝調之路）.
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）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（吴三桂）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.