Baocheng, or Treasure Town, is a wall structure for the protection of the underground palace. Compared with Tai and Kang tombs and other mausoleums, the grave mound within the Baocheng of Zhaoling Tomb is higher and thicker, and an enclosed wall was built accordingly to protect the grave mound. Being linked up with the wall of Baocheng on the two sides of the Square City, the enclosed wall forms a closed courtyard, which is called Mute Courtyard. Because the wall around looks like a crescent, thus it was called “Crescent City”. The later-built Ming mausoleums, Qingling Tomb and Deling Tomb, and the mausoleums of the Qing Dynasty all followed this style and system.