The Great Wall of China is an ancient wall in China. The wall is made of cement, rocks, bricks, and powdered dirt. 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 Qin wall are made of compacted dirt and stone. This the earliest part of the wall was built by Qin Shihuangdi, the first emperor.  Later in the Ming Dynasty they used bricks. There are 7,000 watch towers, block houses for soldiers and beacons to send smoke signals.

Qin built section of the Wall	Ming section of the Wall