For the Chinese, the Great Wall is the spirit and backbone of their civilization. For people around the world, it is the symbol of China. The Great Wall was built by more than 20 dynasties over a time span of more than 2000 years and extended nearly 4000 miles. Initially intended as a military defense system, it consisted of thousands of passes, watchtowers, barracks, and beacon towers. This immense feat of construction is recognized around the world as one of the most important landmarks of China's ancient civilization.