The Great Wall, symbolizing China's ancient civilization, is one of the world's most renowned projects. It is the longest defensive wall in the world. In 1987, UNESCO put the Great Wall on the list of World Culture Heritage. Construction of the Great Wall started from 7th century BC. At that time there were many kingdoms under the Zhou Dynasty.Each kingdom built its own wall around its territory for self-protection. The earliest Great Wall emerged in the Chinese history was the walls of Kingdom Qi and Chu. In 221 BC, Emperor Qinshihuang defeated the other six kingdoms and unified China. He ordered to link up the separated walls and extended them. It started from Lin Tao in the west to Liao Dong in the east, thus a wall of 7,000 kilometers long formed. This became the first climax of building the Great Wall in Chinese history. The second climax of constuction on the Great Wall is the Han Dynasty. For increasing strategic defence and for protecting the newly opened silk roads, the Great Wall of ten thousand kilometers long was constructed. It ran from Xinjing in the west to Liao Dong in the east and became the longest Great Wall in Chinese history. The Han Dynasty was the second climax of construction on the Great Wall. The Great Wall in the Ming Dynasty had been consolidated. It started from the Tiger Hill at the bank of Yalu River of Liao Ning Province to Jiayuguan Pass of Gansu Province in the west, totally 7,000 kilometers long. It went through nine provinces, autonomous regions and municipalities today.