The bi disc is prescribed in the Western Han dynasty (206-8 B.C.E.) Book of Rites as one of six ritual jade shapes in ancient China, although they are also found in burials dating to 2500 B.C.E. Although the meaning of the discs was unclear even in the earliest written records, it is thought that the circular shape was a reference to heaven. By the eighteenth century, bi discs were appreciated more as an expression of antiquarian tastes than for there associations with the cosmos. Whereas the inherent connotations of the bi fluctuated over the millennia, the form remained consistent.
Click here for an example of a Neolithic period jade, currently in the collection of the University of Durham.