After Qin Emperor Shihuang unified China, he sent forces led by general Meng Tian to suppress the Huns, and gained much land. In order to guard against the attacks from the Huns, Meng Tian led soldiers to build the world-renowned Great Wall.

In the Warring States Period (475-221BC), many states built the Great Wall as fortification. The states of Qin, Zhao and Yan all once built some sections to resist the Huns invasions. It was not until the Qin Dynasty (221-206BC) that Meng Tian connected the separate walls to form a defensive system on the northern border. It took about nine years to finish and the wall stretched from Linzhao (in the eastern part of today's Gansu Province) in the west to Liaodong (in today's Jilin Province) in the east. The 5,000-kilometer-long wall not only served as a defense in the north but also symbolized the power of the emperor.

Further construction and extensions were made in the successive Han (206BC-220AD), Northern Wei (386-534), Northern Qi (550-577) and Sui (581-618) dynasties. And in terms of both length and quality, the later constructions were better than that made in Qin.

The present Great Wall in Beijing is mainly remains from the Ming Dynasty (1368-1644). During this period, bricks and granite were used when the workers laid the foundation of the wall and sophisticated designs and passes were built in the places of strategic importance. To strengthen the military control of the northern frontiers, the Ming authorities divided the Great Wall into nine zones and placed each under the control of a Zhen (garrison headquarters). The Ming Wall starts from Yalujiang River (in today's Heilongjiang Province), via today's Liaoning, Hebei, Inner Mongolia, Shanxi, Shaanxi, Ningxia, to Guansu. The total length reaches 12,700 li (over 5,000 kilometers). The Shanhaiguan Pass and the Jiayuguan Pass are two well-preserved passes at either end. Its height varied from 5 to 10 meters and watch houses were built every 130 meters. If enemies came to invade, hays blended with wolf shit was burn in the daytime, the smoke of which would rise very high so that sentinels could get the warn. At night, firewood combined with sulphur would make so bright a fire that sentinels miles away could get noticed.

We can see the remains of the Qin Wall today. Five miles to the northwest of Datong in Shanxi Province there is a purple wall whose name is Purple Pass. And ten kilometers west to the Minxian city in Gansu Province we can also find remains of the Qin Wall. The famous Badaling Great Wall we see today was built in the Ming Dynasty.