It is easy to walk past such a fragment without recognising it for what it is, yet this modest arrangement of stones is the surviving remnant of a wedge tomb, one of the most widespread megalithic monument types in Ireland. Wedge tombs, so called because their chambers taper in both height and width from one end to the other, were constructed during the late Neolithic and into the early Bronze Age, roughly between 2500 and 2000 BC, and are found in greatest numbers in the west and north of the country.

What remains at Greagh is spare but legible to the careful eye. The principal stone, oriented northeast to southwest, stands between one and 1.1 metres high and stretches 2.5 metres in length; it formed the southeast side of the chamber. Some 1.6 metres to the northwest, two small earthfast stones, the largest reaching just 0.7 metres in height, represent the opposite side of what would have been an enclosed burial space. The chamber itself was once roofed and likely covered by a cairn of stones or earth, all of which has long since disappeared. What is left is the skeleton of a structure, reduced by millennia of weathering, agricultural clearance, and the slow persistence of gravity on a sloping hillside.