A tumulus (plural tumuli) is a mound of earth and stones raised over a grave or graves. Tumuli also are known as barrows, burial mounds, Hügelgräber, or kurgans, and may be found throughout much of the world. A cairn, which is a mound of stones built for various purposes, might also originally have been a tumulus. Tumuli are often categorized according to their external apparent shape. In this respect, a long barrow is a long tumulus, usually constructed on top of several burials, such as passage graves. A round barrow is a round tumulus, also commonly constructed on top of burials. The internal structure and architecture of both long and round barrows has a broad range, the categorization only refers to the external apparent shape.The method of inhumation may involve a dolmen, a cist, a mortuary enclosure, a mortuary house, or a chamber tomb. Examples of barrows include Duggleby Howe and Maeshowe.The word tumulus is Latin for 'mound' or 'small hill', which is derived from the Proto-Indo-European root *teuh2- with extended zero grade *tum-, 'to bulge, swell' also found in tumor, thumb, thigh, and thousand.