Flying over the Great Wall of China.

The Great Wall of China is the biggest object ever made by humans. It stretches across mountains, deserts and grasslands for over 6,000 kilometres. The ancient Chinese built the wall to keep invaders from the west out of their country. Today tourists from all over the world come and see it. The Great Wall began as a series of many smaller walls that were not connected with each other. The first sections of the wall were built as early as 600 B.C. As time went on Chinese emperors connected them together to keep Huns, Mongols and other tribes out. Thousands of soldiers, criminals and peasants worked on building the wall. It was finally completed during the Ming dynasty in the 17 th century...