The caisson is generally a sunken panel set into the otherwise largely flat ceiling. It is often layered and richly decorated. Common shapes include square, octagon, hexagon, circle, and a combination of these.
The ''caisson'' is a general name for any sunken panel placed in the ceiling. In the case of East Asian architecture, however, the caisson is characterised by highly developed conventions as to its structure and placement.
These are the following:
The caisson is a sunken panel placed in the centre of the ceiling. It is raised above the level of the ceiling through the use the ''dougong'' structure, which, through interlocking structural members, as beams were not used, creates successive levels of diminishing size. Beams may also be used to create a hexagonal or octagonal caisson surrounded by a square border. These beams, and the ''dougong'' members, are usually visible, and richly carved and often painted with deities.
The centre of the caisson is decorated with a large ''bas-relief'' carving or painting. Common themes include "two s chasing the pearl. Caissons in the throne rooms of the Forbidden City feature a large, writhing dragon, from whose mouth issue a chandelier-like structure called the Yellow Emperor Mirror, a series of metal balls which are said to be able to show reflections of evil spirits.
Caissons were originally used to support s. Therefore they are a relatively recent structure in the Chinese architectural history. However, they became increasingly intricate and formalised, and were in later periods a standard item of interior decoration in formal buildings.
Use in other structures
The caisson has been found in tombs of the Han Dynasty dating the use of this architectural feature back at least 2,000 years. Besides subterranean structure, the oldest existent caisson in an above-ground structure is the one located above the 16 m tall statue of Guanyin in the Guanyin Pavilion of Dule Monastery, Jixian, Hebei province, built in the year 984 during the Liao Dynasty. Without the use of interior columns, this ceiling is held up by a hidden second floor four-sided frame with a hexagonal ceiling frame on the third floor.
As the caisson became increasingly standard in formal architecture in ancient China, similar structures also appeared in grottos, such as in Dunhuang. These sunken panels in the ceiling of grottos would be carved to imitate the ''dougong''-based structure in wooden buildings.
Caissons where highly decorative and used only for the most richly decorated structures. They had no specific cultural significance, since in structure they are equal to cupolas and domes constructed around the world. However the rich oramentation often conveyed cultural significance in the themes chosen.