The Great Wall of China is the longest structure ever built by man. It is about 4,500 miles (7,240km) long, and was built entirely by hand. Part of the Great Wall was built during the Qin Dynasty, but the majority of it was built during the Ming Dynasty (1368-1644) to keep out nomads, thief, spies, and enemy soldiers, but primarily to keep out the Mongols (Mongolian people). It stretches from the eastern-China city of Shanhaiguan to the Lop Nur region of the Xinjiang province. Parts of the great wall have crumbled or eroded over the years, but most of these sections have been restored.