A mythology is a collection of traditional tales, usually of a particular people (such as the ancient Greeks, Indians, or Norsemen), handed down orally through the generations. Most mythologies are of earlier date than the invention of writing in cultures from which they spring. There are three main classes of myths: myths proper, which are imaginative and serious attempts to explain natural phenomena and are often concerned with gods and supernatural events occurring in a timeless past; folk tales, including fairy tales, which are narrative stories in historical time of social concerns; and sagas and legends, which recount embellished exploits of heroes of the past who may or may not have existed. Although most of the cultures of primitive peoples have mythologies not all people do: one example is the Romans, who appear to have had very little in the way of oral tradition, but who borrowed and adapted Greek mythology. The term mythology is also applied to the study of such tales, from which past cultural exchanges can be inferred and historical archeological sites can often be identified. The most famous such study was James Frazer's The Golden Bough (1890) which contains an extensive synthesis of many disparate myths and mythologies.