The Imperial Vault of Heaven
North of the Circular Mound Altar is the Imperial Vault of Heaven, which was originally built in 1530 and rebuilt 1752. Its structure is made from wood and brick with a blue tiled roof that is topped with a gilded ball. It is 19. 5 meters high and 15; 6 meters in diameter. From a distance, the Imperial Vault of Heaven looks like a small version of the Hall of Prayer for Good Harvest.
As you can see, the building does not have any horizontal beams as support. The entire building is supported by 8 pillars and a span-work of bars, laths and brackets, which is in complete conformity with the principles of dynamics. The decorative painted appear fresh because they were retouched in 1974.
In the center of the Imperial Vault of Heaven stands the shrine where the tablet of God of Heaven was placed. There are four stone platforms one each side where the tablets of the emperor s eight ancestors were kept. During each winter solstice, these tablets were placed in a small pavilion-like cage and removed to the Circular Mound for the Worshipping Heaven ceremony. After the ceremony, the tablets were returned to the stone platforms.
Two chambers located at the front of the Imperial Vault of Heaven contained different tablets used for worship. The left chamber contained tablets of the gods of basic elements including gold, wood, water, fire and earth. The right chamber contained tablets of gods of natural phonemena including wind, rain, thunder, lightning and so on.