The Great Wall of China was first constructed in the 7th and 6th century B.C., but it was not completely finished until 200 B.C. Much of the present wall comes courtesy of the Ming dynasty, which reconstructed the old wall around 1500 A.D. to create the modern version of the Great Wall.
Keeping Out Foreign Marauders
One of the main problems for the Chinese were the marauding horsemen called the Mongols, who would attack from the great steppes that lay to the north and west of the Chinese kingdom. They were a constant threat until the Great Wall was put up.
Containing the Home Population
The Great Wall had the added advantage of defining the border of ancient China. The distinctive boundary was easily recognized by the local citizens, who lived inside the wall.
Show of Strength
Construction of the wall showed that the ruling dynasty was a very powerful entity. This in itself might act as a deterrent to foreign invaders.
The Great Wall served as a lookout post for potential military threats and to observe what was going on outside the boundaries of the wall. This became especially important during the glory days of the Silk Road (600-900 A.D.), when European traders were trying to bring western trade and influence to China.
Symbol of National Unity
Even today, the Great Wall serves as a symbol of unity for the country. This was made very evident in 1972, when the president of the United States, Richard Nixon, visited the Great Wall. He is quoted to have said, "I think that you would have to conclude that this is a great wall, and it had to be built by a great people."