China

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 in part to protect the Chinese Empire or its prototypical states against intrusions by various nomadic groups or military incursions by various warlike peoples or forces. Several walls were being built as early as the 7th century, later joined together and made bigger and stronger, are now collectively referred to as the Great Wall. Especially famous is the wall built between 220–206 by the first Emperor of China, Qin Shi Huang. 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 are from the Ming Dynasty.

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, signaling 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 main Great Wall line 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 measure 8,850 km. This is made up of 6,259 km sections of actual wall, 359 km of trenches and 2,232 km 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.

The history of the Great Wall is said to start from the Spring and Autumn Periods when seven powerful states appeared at the same time. In order to defend themselves, they all built walls and stationed troops on the borders. At that time, the total length of the wall had already reached 3,107 miles, belonging to different states.

In 221 BC (Before Chirst), the Emperor Qin absorbed the other six states and set up the first unified kingdom in Chinese history. In order to strengthen his newly born authority and defend the Huns in the north, he ordered connecting the walls once built by the other states as well as adding some sections of his own. Thus was formed the long Qin's Great Wall which started from the east of today's Liaoning Province and ended at Lintao, Gansu Province.

In the Western Han Dynasty, the Huns became more powerful. The Han court started to build more walls on a larger scale in order to consolidate the frontier. In the west, the wall along the Hexi corridor, Yumenguan Pass, and Yangguan Pass was built. In the north, Yanmenguan Pass and Niangziguan Pass in Shanxi were set up. Many more sections of the wall extended to Yinshan Mountain and half of the ancient Silk Road was along the Han's wall.

The Northern Wei, Northern Qi and Northern Zhou Dynasties all built their own sections but on a smaller scale than the walls in the Han Dynasty. The powerful Tang Dynasty saw peace between the northern tribes and central China most of the time, so few wall sections were built in this period.

The Ming Dynasty is the peak of wall building in Chinese history. The Ming suffered a lot by disturbances from minority tribes such as the Dadan, Tufan and Nuzhen. The Ming court from its first emperor to the last ceaselessly built walls in the north. The main line started from Jiuliancheng near the Yalu River in the east to the Jiayuguan Pass in the west and measured over 4,600 miles. Besides adding many more miles of its own, the Ming emperors ordered enlargement of the walls of previous dynasties into double-line or multi-line walls. For example, out of Yanmenguan Pass were added three big stone walls and 23 small ones. Eleven Garrisons were distributed along the main line of the wall. The countless walls, fortresses, and watch towers made the country strongly fortified. In the early Qing Dynasty, some sections of the walls were repaired and several sections were extended. This great engineering work stopped in the middle of the Qing Dynasty.