The Forbidden City is also known as the Forbidden City. In ancient China, the planning concept of "the unity of heaven and man" was emphasized, and the stars in the sky were used to correspond with the capital planning to highlight the legitimacy of the regime and the supremacy of imperial power. The Emperor of Heaven lived in Ziwei Palace, and the emperor of the world boasted that he was the "Son of Heaven" who was ordered by heaven. His residence should symbolize the Ziwei Palace to correspond with the Emperor of Heaven. The Book of the Later Han Dynasty recorded that "there is a Ziwei Palace in heaven, which is the residence of God. The king set up the palace, and acted like it". Ziwei, Ziyuan, Zigong and so on became synonymous with the imperial palace. Because the feudal imperial palace was a forbidden area in ancient times, ordinary people could not enter it, so it was called "Forbidden City". In the early Ming Dynasty, together with the Outer Forbidden City, they were collectively called "Imperial City". About the middle and late Ming Dynasty, they were distinguished from the Outer Forbidden City, that is, the Palace City was called "Forbidden City", and the Outer Forbidden City was called "Imperial City".