The name "Zijin Cheng" is a name with significance on many levels. Zi, or "Purple", refers to the North Star, which in ancient China was called the Ziwei Star, and in traditional Chinese astrology was the heavenly abode of the Celestial Emperor. The surrounding celestial region, the Ziwei Enclosure (Chinese: 紫微垣; pinyin: Zǐwēiyuán), was the realm of the Celestial Emperor and his family. The Forbidden City, as the residence of the terrestrial emperor, was its earthly counterpart. Jin refers to a prohibition or taboo (often used in signs saying "no entry" or "no smoking" or "X is prohibited"). Cheng originally meant a castle, fortress, or fortification, but in modern Chinese, the character means city.