|Boromir: "Is it not a strange fate that we should suffer so much fear and doubt for so small a thing? So small a thing!"|
- J. R. R. Tolkien, The Fellowship of the Ring II:10
A barrow (more properly, a type of tumulus) is an artificial mound of earth and/or stones built up over a grave(s), and is an ancient and fairly widespread form of inhumation. Burial in barrows seems to have been common among the early Edain, at least for the nobility, and the practice was continued (or revived) by the Dúnedain of Arnor, Arthedain, and Cardolan.
Famous barrows include those on the Barrow-downs (S: "Tyrn Gorthad") and the Kings' Barrows ("Barrowfield") outside Edoras in Rohan, but these groups are just two of many in Middle-earth.