The Nanjing City Wall (Ming City Wall was initially built in the 26th year of the reign of Zhizheng(AD 1366)in the Yuan Dynasty. It was built on the trend of mountains and rivers on the basis of the historical city walls. The layout of the city was irregular, and it took two stages of initial construction and reinforcement and expansion. It was completed in the 26th year of the reign of Hongwu(AD 1393) in the Ming Dynasty, with a construction period of 28 years.Millions of craftsmen and civilian workers across the country went to the capital city to build the city wall. Eventually formed the complete form of four layers of city, namely, Palace City, Imperial City, Capital City and Outer City Wall from the inside out, which has become a classic work in the building history of ancient capital in China.