The Great Wall of China is a long series of fortifications built along an east-to-west line across the historical northern borders of China to protect the empire against invasions from north. Like a gigantic serpent, the wall winds up and down across mountains, valleys, deserts and jungles, covering a length of 8851.8 km. It is listed as a UNESCO World Heritage Site.
Construction for the Great Wall of China started in 220 BC by Qin Shi Huang, the first emperor of China who conquered neighboring states and unified the country. Since then it was continuously built and restored by successive kingdoms till the 1700s. What we see of the wall today was constructed mostly during the time of the Ming dynasty which revived the walls after facing reverses in wars with the Manchurian and Mongolian tribes.
The purpose of construction of the wall was to keep the barbarian invaders from north at bay. With time, it also served as an instrument of border control, excise regulation and emigration barriers. Up to 25,000 watch towers were constructed for the purpose of vigil and defense.
With the fall of the Ming empire in 1644 AD, the boundaries of the victorious Qing dynasty spread much beyond the wall and it lost its strategic importance. Much of the wall fell in neglect and disrepair and was not revived till the 20th century when attempts at its conservation began.
The human cost of building the Great Wall of China was great. Millions of peasants, workers, soldiers and prisoners toiled for centuries to built these walls and hundreds of thousands of them perished during the construction.