 The whole temple complex is surrounded by two cordons of walls; the outer wall has a taller, semi-circular northern end, representing Heaven, and a shorter, rectangular southern end, representing the Earth.Both the Hall of Prayer for Good Harvests and the Circular Mound Altar are round, each standing on a square yard, again representing Heaven and Earth.The number nine represents the Emperor and is evident in the design of the Circular Mound Altar