The excavation of two adjacent round barrows at Trelystan, Long Mountain, Powys, in 1979, has revealed a complex sequence of Late Neolithic and Early Bronze Age funerary structures and traces of Late Neolithic settlement. The earliest structure was a large pit grave, dated to about 2400 bc, which was superseded at about 2200 bc by a settlement represented by stake-walled buildings associated with Grooved Ware. Following this some activity took place, possibly domestic, which is represented by sherds probably derived from several southern Beakers, which by analogy with sites elsewhere are to be dated to a period after about 1850 bc. The subsequent Bronze Age cemetery, dated to between about 1800 and 1500 bc (but possibly continuing later), presents a sequence of burial types and structures which can broadly be seen to illustrate a change from the concept of barrow cemetery to that of cemetery barrow. The earliest burials, which consist of cremations in pits and occasionally accompanied by a Food Vessel, were covered by separate small mounds of stone or turf, or a combination of the two. These were eventually overlain by and amalgamated beneath two larger turf barrows associated with Food Vessel Urns, which employed stake circles in their construction and which acted as repositories for additional cremation burials. The cemetery was sited along a pre-existing boundary fence, set up after the Late Neolithic phase, which was renewed at various times throughout the life of the cemetery in response to changes in its layout. A small undated cemetery of inhumation graves, possibly of the Early Christian period, was founded on the eastern side of the barrows at a later date.