The one at Rosbeg in County Mayo is among them, a megalithic structure whose popular name ties it to one of the most persistent stories in Irish mythology, the tale of Diarmuid and Gráinne, the doomed lovers said to have fled across the country pursued by the ageing hero Fionn Mac Cumhaill. Any large flat stone resting on uprights, the form known as a portal tomb or dolmen, could become their bed for the night in local tradition, and the name stuck to dozens of sites regardless of their actual type or date.

The monument at Rosbeg was recorded and described by Ruaidhrí de Valera and Seán Ó Nualláin in their 1964 survey of the megalithic tombs of County Mayo, part of a landmark multi-volume catalogue of prehistoric funerary monuments across Ireland. Megalithic tombs, built from large stones during the Neolithic and into the early Bronze Age, served as communal burial places and sometimes as focal points for ritual activity over generations. The Rosbeg example falls within this broader tradition of monument-building in County Mayo, a county that preserves a remarkable concentration of such structures, from court tombs to passage tombs to wedge tombs, each type reflecting different periods and practices.

Beyond the survey reference, the specific structural details of the Rosbeg monument are not well documented in available sources, which means the site rewards careful attention on the ground more than it does advance reading. The name itself, wherever it appears on a hillside or in a field, is worth pausing over, less as a guide to mythology and more as a record of how ordinary people in rural Ireland folded the deep past into familiar stories, giving nameless ancient stones a human drama to explain their presence in the landscape.