The name of the Forbidden City comes from the metaphor of the Ziwei Star Altar. Ancient Chinese astronomers once divided the stars in the sky into three constellations, twenty-eight stars and other constellations. The three walls include Taiweiyuan, Ziweiyuan and Tianshiyuan. Ziwei Yuan is in the center of the three walls. According to ancient Chinese astronomy, based on long-term observations of celestial bodies in space, it is believed that the Ziwei star cluster resides in the middle of the sky and its position remains unchanged forever, so it has become a constellation representing the Emperor of Heaven. It is the residence of the Emperor of Heaven. Therefore, the Heavenly Palace where the Emperor of Heaven lives is called the Purple Palace, and there is a saying that "Zi Wei is in the middle".
The feudal emperors claimed to be the sons of the Emperor of Heaven and considered themselves the real Dragon Emperor; and the palace where they lived was likened to the Purple Palace in the sky. They also hope that if they live in the Purple Palace, they can govern with virtue, be naturalized from all directions, and come to court from all directions, so as to achieve the goal of lasting stability and long-term rule.
The emperors of the Ming and Qing dynasties, in order to maintain their own authority and dignity and consider their own safety, built palaces that were both magnificent and fortified. This city not only has many palaces and pavilions, but is also surrounded by a 10-meter-high city wall and a 52-meter-wide moat. It is also heavily guarded with sentry posts. Common people are not allowed to even look at the towers and palaces, even if they get closer.
In addition to the maids, eunuchs, and guards who served them, only summoned officials and authorized personnel could enter the palace where the emperors of the Ming and Qing dynasties and their families lived. Outsiders were not allowed to enter the palace. A place that is one step beyond the thunder pool. Therefore, the imperial palaces of the Ming and Qing dynasties were both called the Purple Palace and forbidden areas, so they were formerly called the Forbidden City.