Temple of heaven - Throne of Heaven

Each circumference around the central slab (which was nothing less than the center of the universe) is a multiple of 9, and in all there are... 9 rings...
This is where the emperor stood during the ceremony. It is said that wishes are fulfilled if you stand on this slab while thinking of your wish, and this is why there is a crowd to get there.
What is for sure is that the acoustic is amplified at the center.