Visitors to an ancient Chinese palace hall often have their attention drawn to the centre of the ceiling. The zaojing or caisson ceiling is a distinctive feature of classical Chinese architecture, if not unique to it. It is usually in the form of a sunken
coffer bordered in a square, a polygon or a circle, decorated with elaborately carved or painted designs. This architectural decoration dates a long way back for it has been found in tombs of the Han Dynasty 2,000 years ago.

One of the most magnificent zaojing is that of Taihedian (Hall of Supreme Harmony) in the old palace of Beijing. Carved and built with consummate skills, its splendour has remained undiminished by time. The caisson consists of three parts of different depths. The central deepest part is the round "well (jing)", the middle part is the octagonal "well", and the outermost part, coming down to the same level as the rest of the ceiling, is a square. The whole design symbolizes the ancient Chinese belief that "Heaven is above and the Earth below" and that "Heaven is round and the Earth square." Dominating the centre of the caisson is a coiled dragon looking down into the hall and holding suspended in its mouth a huge silver-white pearl. It vies for glamour with the gilded dragons on the columns, giving the throne hall a colourful yet solemn nobility not to be found elsewhere.

The Chinese name for the caisson ceiling, zaojing, means "aquatic plants" (zao) and "well" (jing), both having to do with water. It was so named because there was constant worry about fire which might destroy the palace buildings. With water from the zaojing, so the ancients believed, the threat of fire would be averted.