Special Caisson Ceiling Designs in the Forbidden City

Caisson ceiling is the unique design of interior ceiling in traditional Chinese Architecture. It is made from wood, generally looking like an open umbrella and decorated with various carvings and colorful paintings, representing the highest architecture level in ancient China. It can only be used in the royal palaces and temples with high ranks, set right above the seats or Buddha statues.
 
In the Forbidden City, there are about 20 caisson ceilings, in the Hall of Supreme Harmony (Taihedian), Palace of Compassion and Tranquility (Cininggong), Palace of Longevity and Health (Shougkangong), Garden of Compassion and Tranquility (Cininggong Garden), Palace of Abstinence (Zhaigong), etc. The Forbidden City, as the best royal architecture in the Ming and Qing Dynasties (1368 - 1912), is extremely exquisite in the construction of this wooden artwork.
 
The shape of the caisson ceilings in the Forbidden City include round, square, oval, spiral and polygon. Most of the time, several shapes are applied in one caisson ceiling, to make the ceilings seem high and far.
 
The caisson ceiling is pile up with mortises, tenon joints, and Dougong. Dougong is a system of brackets inserted between the top of a column and a crossbeam. Not a single nail is used.
 
In the middle of the caisson ceiling, is usually a big wood carving in the shape of a dragon to symbolize the supreme power of the emperor. Below the dragon, is a Xuanyuan Mirror to drive off evil spirits. Surrounding them are patterns of algae and aquatic plants. They are usually glazed with gold or painted green.
 The caisson ceiling actually has something to do with the fire fighting. A special ceiling is made at the top of the palace and the pavilion, and decorated with algae and aquatic plants patterns such as lotus, water chestnut, lotus root in the hope of subduing the fire devil and protecting the safety of the building.
 The caisson ceiling in the Hall of Supreme Harmony has three layers in round, octagonal, and square shapes from top to bottom. This kind of design just embodies the traditional Chinese conception of round sky and square ground. A finely carved golden dragon spins in the center with a Xuanyuan Mirror below and looks down. Together with the golden dragons on the huge columns in the hall, they highlight the majesty and magnificence of the highest-ranked building in the Forbidden City.
 
The caisson ceiling in the Palace of Compassion and Tranquility looks very small, which is inharmonious with the spacious palace. The reason relies on the reconstruction of the palace. At first, the Emperor Qianlong upgraded it and added a caisson ceiling to make it a ceremonial palace.  Later, a double-eave roof was built but this time the reconstruction didn't include the caisson ceiling. When the original caisson was raised, it looked smaller on the new roof. In addition, the Xuanyuan Mirror under the caisson ceiling is not in conventional spherical shape, but resembling a round ball inside a cube. This kind of Xuanyuan Mirror can be seen nowhere else. Maybe it also implies the meaning of “round sky and square ground” in ancient Chinese conception.
 
A special painted caisson ceiling can be found in the Linxi Pavilion of the Garden of Compassion and Tranquility. It is gilded and drew with colorful paintings to make the pavilion grand and magnificent. This is the only painted caisson ceiling in the Forbidden City.