Nanjing City Wall

The Nanjing City Wall is the city wall of Nanjing, China. Most of it was made during the early Ming Dynasty, when Nanjing was the capital of China.
The city wall has a Jingshiying Tianfu four city wall pattern. It consists of four walls: namely, the imperial city, the imperial city, the capital city, and the outer city. Now, the name mainly refers to the well-preserved capital city wall, which is the longest, largest, and best-preserved old city wall in the world, with a total preserved length of 25.1 km. 
The city wall you see in Nanjing today was built in 1366 (Yuan to Zheng 26 years) and completed in 1393 (Ming Hongwu 26 years), 27 years in all. Building it used 1 ministry, 3 weis, 5 provinces, 28 prefectures, and 152 prefectures and counties. A total of 280,000 migrant workers made it using about 350 million urban bricks.
Its gates include the Gate of China, the Zhongshan Gate, and the Xuanwu Gate.