Great Wall of China

The Great Wall of China is the longest man-made structure ever built, stretching approximately 21,196 kilometers (13,171 miles) from the eastern coast to the Gobi Desert. Construction began in the 7th century BCE and continued through the Ming Dynasty (1368-1644), when most of the current wall was built. The Wall was constructed to defend Chinese states and empires against nomadic raids from the Eurasian Steppe. At various times it also served as a transportation corridor and a means of controlling immigration, emigration, and trade. Building the Wall required extraordinary human effort. Hundreds of thousands of workers — soldiers, peasants, and prisoners — died during construction. Many were buried within the Wall itself, earning it the grim nickname "the longest cemetery on Earth." Today it is one of the world's most visited historical monuments and a UNESCO World Heritage Site. Despite popular belief, it is NOT visible from space with the naked eye.