Megalithic monuments, a broad category covering everything from portal tombs and passage graves to standing stones and court cairns, were raised across Ireland during the Neolithic and Bronze Age periods, roughly five thousand to three thousand years ago. Mayo is unusually rich in such remains, partly because the county's thin soils and lower population density allowed many structures to survive that were cleared or quarried away elsewhere. What exactly stands at Coollisduff, whether a collapsed tomb, an alignment of stones, or something stranger and harder to categorise, remains, for the moment, a question without a publicly available answer.