The Great Wall of China

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, 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.

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 had already been begun to be built beginning around the 7th century BC; these, later joined together and made bigger, stronger, and unified are now collectively referred to as the Great Wall.

Other purposes of the Great Wall have included allowing for border control practices, such as check points allowing for the various imperial governments of China to tariff goods transported along the Silk Road, to regulate or encourage trade (for example trade between horses and silk products), as well as generally to control 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 smoke or fire, and the fact that the path of the Great Wall also served as a transportation corridor.

The Great Wall of China is not a continuous wall but is a collection of short walls that often follow the crest of hills on the southern edge of the Mongolian plain. The Great Wall of China, known as "long Wall of 10,000 Li" in China, extends about 8,850 kilometers (5,500 miles).

A first set of walls, designed to keep Mongol nomads out of China, were built of earth and stones in wood frames during the Qin Dynasty