The Great Wall of China snakes across China for thousands of kilometres. Despite what you'll read in many books, there is no set length of the Great Wall. The Wall is not just one wall. It was originally lots of different defensive walls built by different Chinese rulers. In 221 B.C., Shi Huang Di, the first emperor of China, wanted to protect his empire so he joined lots of pieces of wall together. Even so, the Wall is still not one long wall. Some segments of the Wall are parallel to each other, some criss-cross, and some are isolated and abandoned.

• The Great Wall, the one joined together by the emperors of the Qin, Han, Jin and Ming Dynasties, is about 5 000 kms long. But altogether, if we added up all the bits of wall built for military purposes over the last 2000 years, there are 50 000 kms of walls in northern China!

• The Great Wall was built across rough country, from deserts to steep mountains and river valleys. The land was already almost impossible to attack. Marching an army and its supply wagons through such rugged isolated country would have been very difficult.

• 1 000 000 prisoners and forced labourers died building the Wall and 1 000 000 soldiers patrolled it once it was built.

• The Wall is built out of whatever material was locally available - stone, bricks, or mud and sticks.

• Thousands of towers were built along the Wall. From these, soldiers could send messages using smoke during the day, and fire at night.