Temple of heaven - Altar of Heaven seen from one side

This is the place of ceremony. The compound is square : a symbol of Earth, while the terrace is circular : a symbol of Heaven.
The figure 9 (symbol of longevity) appears in a variety of forms.
In China, the figure 9 is a homonym for "sustainable". Moreover, even numbers are associated with yin (like the land) while odd numbers are associated with yang (like the sky, see that !). Let's notice that 9 is the largest odd figure... and that as the emperor was the "son" of Heaven in Chinese cosmogony, the symbolic use of this figure was reserved for him.