Introduction to the Wengcheng: The Wengcheng was built in a small city outside the city gate, also called the Moon City, to enhance the city's defense capabilities. "Wu Jing Zong Yao First Collection: Guarding the City" records: "The urn outside the city is either round or square. Depending on the terrain, it is as high and thick as the city, but one door is left open, and the left and right are as they please." Pingyao Ancient City Most of the Wengcheng gates and the main city gate are oriented at an angle of 90° (except for the South Gate and Lower East Gate). Even if the enemy breaks through the Wengcheng gate, there is still a main city gate defense, which is not easy to deploy due to the narrow space in Wengcheng. The large-scale attack slowed down the enemy's attack, while the defenders at the top of the city wall could shoot from all directions, dealing a fatal blow to the enemy. It was the so-called catching a turtle in a urn.