中国古代天文学家曾把天上的恒星分为三垣、二十八宿和其他星座。三垣包括太微垣、紫微垣和天市垣。古代天文学认为紫微垣居于中天,位置永恒不变,因此成了代表天帝的星座,是天帝所居,因而,把天帝所居的天宫谓之紧宫。而禁,意指皇宫乃是皇家重地,闲杂人等不得来此。明清两代的皇帝,出于维护权威以及自身安全的考虑,所修建的皇宫壁垒森严。这座城池,不仅宫殿重 Ancient Chinese astronomers have divided the stars of heaven into Mianyuan, Ershibasu and other constellations. Miyaki include Taiyuan, Ziwei and Tianshiyuan. Ancient astrology believes that Zi Weiyuan live in transit, the location of eternity, it has become the constellation of the Emperor of Heaven, is the emperor, and therefore, the heavenly palace of Heavenly Palace that the impending palace. The ban, which means that the Royal Palace is a royal place, such as miscellaneous people can not come here. Ming and Qing dynasties, the emperor, out of the maintenance of authority and their own safety considerations, the palace built by the heavily guarded. This city, not only palace heavy