Inscribed turtle plastron, Shang dynasty, 12th century B.C., The Institute of Archaeology, CASS, Beijing. Diviners used the natural symmetry of the shell -- designating one side as a positive answer and the other as a negative answer. After heat was applied, a crack would form, pointing to the correct answer. Later legend held that it was the markings on a carapace that first revealed the secrets of divination to mankind.

Shang kings used oracle bones to divine answers to various questions concerning the success of harvests, military expeditions, events such as the birth of a child, and even very personal matters such as which disaffected ancestor might be causing a toothache. The bones (some imported as tribute) were cleaned and carved with a series of grooves. Heat was then applied to a groove, causing small cracks in the bone, which were interpreted by a diviner. Questions and, in some cases, outcomes were recorded on the bone, the inscriptions sometimes highlighted with black or red ink. These inscriptions constitute the first historical writing to have survived from ancient China.

All extant oracle bones come from late Shang-period sites around Anyang. This one was found at Xiaotun, where oracle bones were stored and buried. The foundations of a large temple-palace found at Xiaotun indicate that it was probably the center of late Shang religious activity.

On this scapula, the hollows prepared for the hot brand are clearly visible. The inscription, running vertically down the right side, records sacrifices performed for ancestors. The divination was, presumably, to ensure that they found the rites acceptable. It reads in part: "to ancestress Yi offer a fine pig, to ancestress Gui a boar, to ancestress Ding a pig, to ancestress Yi a pig."

The ancestors are called by their temple names, which were assigned to them posthumously and correspond to the names of days of the week (a week consisted of ten days). In this way the Shang were able to schedule ancestral sacrifices on the appropriate day.