Under Lingxing Gates, Circular Mound Altar Entering through the Zhaoheng Gate (the southern gate), you will see a white marble road stretching out to the Circular Mound Altar. It is enclosed with two walls; the inner one is circular symbolizing heaven and the outer one is square symbolizing the earth. The two walls reflect an ancient Chinese thought that ‘heaven is round and the earth is square’. The tops of the walls are covered with green glazed tiles. 24 groups of Lingxing Gates are set around the walls. Each group includes three openings - the middle one, a special passage for the Heaven Great being the biggest; the west one for the emperor is smaller; the east one is the smallest, and is used for the accompanying personnel for the worship ceremony.