Introduction to Zhonghua Gate Castle: Zhonghua Gate, known as Jubao Gate in ancient times, is the south gate of Nanjing, the capital of the Ming Dynasty. The Zhonghuamen Urn City in Nanjing is the largest existing castle-style urn city in China and the best-preserved ancient castle with the most complex structure in the world. The Zhonghuamen Castle has a strict layout and unique structure. It is composed of three urn cities and has a "mou"-shaped structure. There are 27 soldier-hiding caves in the entire city, which can hide more than 3,000 soldiers. It has become an important physical material for studying ancient military facilities in my country.