[2] Interest in the jade shape developed during the 12th–13th century Song dynasty.

[3] A cong is a straight tube with a circular bore and square outer section with more or less convex sides.

The outer surface is divided vertically or horizontally such that the whole defines a hollow cylinder embedded in a partial rectangular block.

Although it is generally considered to be a ritual object of some sort, the original function and meaning of the cong are unknown.

Later writings speak of the cong as symbolizing the earth, while the bi represents the heavens.