Jade-cong and Jade-bi were produced by the Liangzhu culture (3400-2250 BC); later examples date mainly from the Shang and Zhou dynasties.
In form, a cong is a tube with a circular inner section and squarish outer section. The outer surface is divided vertically or horizontally such that the whole defines a hollow cylinder embedded in a partial rectangular block. Proportions vary - a cong may be squat or taller than it is wide. The outer faces are sometimes decorated with masklike faces, which may be related to the taotie designs found on later bronze vessels.
A bi is a flat jade disc with a circular hole in the centre. Neolithic bi are undecorated, while those of later periods of China, like the Zhou dynasty, bear increasingly ornate surface carving (particularly in a hexagonal pattern) whose motifs represented deities associated with the sky (four directions) as well as standing for qualities and powers the wearer wanted to invoke or embody.
Although generally considered to be a ritual object of some sort, the original function and meaning of the cong and bi are unknown. Later writings speak of the cong as symbolizing the earth, while the bi represents the heavens. The square represents the earth and a circle represents the heavens.