The Great Wall of China is the longest structure ever built. It was constructed to keep out invaders. The Great Wall, which is made of stone and brick, extends for about 6,400 kilometres. It follows a winding course that stretches over mountains and hills and along the borders of deserts. Only man made structure can be seen from the space. Thousands of people lost their lives during the construction.

Through the centuries, much of the Great Wall again collapsed. However, the Chinese Communists have done restoration work since 1949, when they began to rule the nation. The wall no longer serves the purpose of defence, but it attracts many visitors from around the world. Scientists study earthquakes by examining parts of the wall that have been affected by these earth movements.