Seen from space?
Contrary to popular belief, it can't be seen from the Moon. It was not built as one long wall - different Chinese dynasties built different walls, and they connect in places. But the Great Wall of China is truly great, and it is one of the places in the world you have to visit.
For many years, people said the Great Wall was around 5,000km long. But in April, a survey found it was actually longer than 8,800km. That's about the same distance as from Los Angeles to Tokyo - 12 hours by plane.
A huge endeavour
The early Chinese states probably built primitive walls seven centuries before the birth of Christ. But they got serious about building after Qin Shi Huang conquered all of China in 221BC. He destroyed all the old walls and built a new one in the north.
Qin Shi Huang's wall, like all the walls that came after it, aimed to keep out the 'barbarian' people who lived on the plains. The Chinese called them the Xiongnu. But they were actually a mix of many different tribes - mostly Turkic and Mongol - who sometimes banded together to try to take over China.
Waves of walls