City wall in Nanjing city, Jiangsu Province (Photo via official website of Nanjing City Wall)
Living history: ancient city walls
As a cradle of civilization, China's first city wall was built some 6,000 years ago during the Neolithic Age. As an indispensable part of the ancient Chinese cities, the city walls served as part of the defense systems as well as the architectural experience. It also had political symbolic significance.
In the ancient times, each city's walls were made of different layers varying in scale and form. There were strict rules for the height, width, as well as the number of gates and towers depending on whether the city was the capital, a provincial capital or a county.