All the ancient arthitectures in China were based on the mistary Feng Shui. Feng shui, a marriage of art and science, is a practice founded in China and refined by feng shui masters through 6,000 years of development. Feng shui masters carefully map the nature and flow of energy through buildings and spaces.
In order to collecting the best luck for the owner of a building, the Feng Shui masters are always to suggest the owner to make their buildings include not only the sky but also the earth. When you have the sky and the earth at the same time, it means you have the entire universe! In ancient Chinese architecture, the circle is symbolic of the heaven and the square the earth.
Well, let me show you two pic for better understanding:
Did you notice the circle of building and square wall around the building?