Ancient astronomers divided the fixed stars into three enclosures, twenty-eight mansions, Purple Forbidden Enclosure, and Heavenly Market Enclosure. The Purple Forbidden Enclosure is at the center, symbolizing the emperor’s residence, hence the term “Purple Forbidden City.” The imperial palace was called the Purple Forbidden Palace, and the roads in the capital were also associated with “purple,” known as Zi Mo 紫陌 [Purple Roads], referring to the city’s roads. Purple represents the color of high-ranking official clothing. In the Tang Dynasty, officials of the third rank and above wore purple, while those of the fifth rank and below wore vermilion. The purple pigment in ancient China was extracted from purple grass. It is hard to get, so purple pigment was also called “imperial purple.”
Wang, K. Q. (1994). “Purple” and Imperial Nobility. Language Knowledge, 05, 38-39. https://doi.org/10.13513/j.cnki.41-1041/h.1994.05.017
