Called Treasure Gate (Jubao Men) in ancient times, the castle-like Zhonghua Gate was the largest gate in the city wall of Nanjing and the biggest castle in China. It is also called Jar Gate (Wong Men) for its jar-shaped ap­pearance, designed to resist attacks from enemies. Inside the castle there are 24 caves that can hold 3,000 soldiers. The gate occupies an impor­tant position in the history of the architecture of Chinese city walls because of its magnificent scale, complex structure, and intelligent design.