The Great Wall of China is an ancient wall in China. It is made of stone, pounded dirt, and other things. It was built to protect the north of the empire of China from enemy attacks. It is the longest structure humans have ever built. It is about 21,196 kilometres (13,171 miles) long, 9.1 metres (30 feet) wide and 15 metres (50 feet) high. The earlier sections on the wall are made of compacted dirt and stone. Later in the Ming Dynasty they used bricks. There are 7,000 watch towers. There are block houses for soldiers. There are beacons to send smoke signals
It passes through Xinjiang Uygur Autonomous Region, Gansu Province, Ningxia Hui Autonomous Region, Shaanxi Province, Shanxi Province, Inner Mongolia Autonomous Region, Hebei Province, and Beijing Municipality
It was initially built during Qin Dynasty (221-207 BCE), which went through expansion, destruction and reconstruction many times, with the latest one built during Ming Dynasty (1368-1644 CE). Its main goal was to keep the invaders from the north out of the China proper, which was sometimes not as effective as most Han Chinese would tell you. Parts of the structures are still standing firm, while others are pretty much in ruins
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