Perhaps the most obvious way artistic creation reflects how people live is by mirroring the environment — the materials and technologies available to a culture. Stone, wood, tree bark, clay, and sand are generally available materials. In addition, depending on the locality, other resources may be accessible: shells, horns, gold, copper, and silver. The different uses to which societies put these materials are of interest to anthropologists who may ask, for example, why people choose to use clay and not copper when both items are available. Although there are no conclusive answers yet, the way in which a society views its environment is sometimes apparent in its choice and use of artistic materials. The use of certain metals, for example, may be reserved for ceremonial objects of special importance. Or the belief in the supernatural powers of a stone or tree may cause a sculptor to be sensitive to that material. What is particularly meaningful to anthropologist is the realization that although the materials available to a society may to some extent limit or influence what it can do artistically, the materials by no means determine what is done. Why do the artists in Japanese society rake sand into patterns; and the artists in Roman society melt sand to form glass? Moreover, even when the same material is used in the same way by members of different societies, the form or style of the work varies enormously from culture to culture. A society may simply choose to represent objects or phenomena that are important to its population. An examination of the art of the Middle Ages tells us something about the medieval preoccupation with theological doctrine. In addition to revealing the primary concerns of a society, the content of that society's art may also reflect the culture's social stratification.