Cheng is a northern beast that eats people like dogs in ancient books. It was first recorded in Erya, and it was recorded as the culmination of a zombie in the note novel Xu Ziyan House in Qing Dynasty, which evolved from See You in Xiuli. On the huabiao in front of Tiananmen Gate, there are two stone tablets facing south, named "Looking at the Emperor's Return". It is said that they pay special attention to the emperor's overseas tour. If the emperor didn't come back after a long tour, they called on him to come back quickly and deal with political affairs. The two stone jars at the back of the gatehouse face south and are called "Wangdi". Their division of labor is different. They monitored the emperor's behavior in the palace. If the emperor lives in the palace, regardless of state affairs, they will urge the emperor to go out of the palace to observe the situation.