The Great Wall of China

The Great Wall of China is the world's longest wall, is 2400km (1500 miles) long, 7m (23') high, and a roadway of 5.5m (18') runs along the top. It was thought that this would be the only structure that would be visible the moon.

The first Chinese emperor build this wall around year -215 during the Qin Dynasty (-221 to -207). Large parts already 200 years old. Shi Huang Di ordered the sections to be joined together to keep out the wild Mongol tribes from the north. Many soldiers, slaves and criminals worked and died on the wall, but does not stop the Mongol army of Genghis Khan in 13th century from invading China.