The Chinese have walled their cities throughout recorded history, and during the Warring States period (around the fifth century BC) simply extended the practice to separate rival territories. The Great Wall’s origins lie in these fractured lines of fortifications and in the vision of the first Emperor Qin Shi Huang who, having unified the empire in the third century BC, joined and extended the disparate sections to form one continuous defence against barbarians.
Under subsequent dynasties, whenever insularity rather than engagement drove foreign policy, the wall continued to be maintained; in response to shifting regional threats, it grew and changed course. It lost importance under the Tang, when borders were extended north, well beyond it. The Tang was, in any case, an outward-looking dynasty that kept the barbarians in check far more cheaply by fostering trade and internal divisions. With the emergence of the insular Ming, however, the wall’s upkeep again became a priority; from the fourteenth to the sixteenth century, military technicians worked on its reconstruction. The Ming wall is the one that you see today.
The 7m-high, 7m-thick wall, with its 25,000 battlements, served to bolster Ming sovereignty for a couple of centuries. It restricted the movement of the nomadic peoples of the distant, non-Han minority regions, preventing plundering raids. Signals made by gunpowder blasts, flags and smoke swiftly sent news of enemy movements to the capital. In the late sixteenth century, a couple of huge Mongol invasions were repelled, at Jinshanling and Badaling. But a wall is only as strong as its guards, and by the seventeenth century the Ming royal house was corrupt and its armies weak; the wall was little hindrance to the invading Manchus. After they had established their own dynasty, the Qing, they let the wall fall into disrepair. Slowly it crumbled away, useful only as a source of building material – demolitions of old hutongs in Beijing have turned up bricks from the wall, marked with the imperial seal.