Why does the Circular Mound Altar use both circular and square walls?

The use of both circular and square walls at the Circular Mound Altar is a deliberate design choice rooted in traditional Chinese architecture.

The layout of the altar, which is enclosed by walls that are square on the outside and round on the inside, serves to symbolize the ancient Chinese belief that heaven is round and the Earth is square. By incorporating these geometric forms, the structure creates an integrated pattern intended to represent the cosmic relationship between heaven and Earth as conceived by architects of the Ming dynasty.12