Why didn't the ancient artillery fire directly at the city gate when attacking the city?

Because, during the war, the ancient city gate was not two door panels, but a solid gate, which was controlled by a winch. When there is an enemy situation, once the city gate is opened, thousands of people can't get in or out. Like Zhengyangmen in Beijing and Zhonghua Gate in Nanjing, they are all typical structures of a thousand-pound lock. Moreover, the ancients were very wise, and the gate structure was often double-layered. If the city gate is captured, the other side will take jiaozi instead.

ancient city

In contrast, the wall is thin!