The City Wall of Nanjing is the longest city wall on the world. It was designed by Emperor Zhu Yuanzhang after he founded the Ming Dynasty and established Nanjing as the capital 600 years ago. The ancient Nanjing city wall was 93.6 kilometers, but only about 70% of its inner part remained, which is 24 kilometers. You can walk on the top of the wall and visit the Zhonghua gate (castle) to see the glory of ancient Nanjing, which was the 6th biggest city in the Chinese history.