Chapter I
What it means
The bi stands for Heaven. The Rites of Zhou, a ritual text of the late first millennium BCE, says that a blue-green bi was used to honour Heaven and a yellow cong, a square tube, to honour Earth: round Heaven and square Earth, the ancient Chinese picture of the cosmos.
Jade itself was prized above gold. It was believed to protect the body, and Confucius compared its qualities to those of the gentleman: smooth, firm, pure.
Chapter II
Where it comes from
The earliest bi come from the Liangzhu culture of the Yangzi delta, about 3300–2300 BCE, where they were laid in great numbers in elite graves. Through the Zhou and Han dynasties bi were used in rites and burials; some Han princes were buried with bi placed on and around the body.
Later emperors performed the sacrifice to Heaven at the round Altar of Heaven in Beijing, where jade discs were among the offerings.
Chapter III
Where you see it today
Ancient bi are treasures of museum collections. Modern jade discs, often worn as pendants, carry wishes for protection and good fortune. The design of the 2008 Beijing Olympic medals included a jade disc inspired by the bi.