The lands east of the Shire and the Old Forest were called the Barrow-downs because of the great funeral barrows built there. They were considered by many during the Third Age to be the most ancient burial ground of Men on Middle-earth.

There were no trees or water on the downlands, only grass covering dome-shaped hills that were ringed and crowned with stone monoliths. They were used by the Dúnedain to bury their dead, but in the Third Age minions of the Witch-king of Angmar began to inhabit the barrows, making them a terrifying place to be. The minions became known as Barrow-wights.

In the TA3018, Frodo Baggins journeyed through the Barrow-downs with his companions, while bearing the One Ring. But for the intervention of Tom Bombadil, Frodo , Sam, Merry and Pippin would certainly have lost their lives to one of the Barrow-wights.
Encyclopedia entry originally written by whats_taters_eh?