Portal tombs, sometimes called dolmens, are among the most visually arresting structures left by Ireland's earliest farming communities; they consist of two tall portal stones flanking an entrance, a lower backstone, and a large capstone tilted at an angle across the whole assembly. They were built as collective burial monuments, probably around 4000 to 3500 BC, and the effort required to raise and position stones of that scale suggests communities with both the social organisation and the motivation to invest enormously in how they treated their dead.

Mayo is not short of prehistoric monuments, but portal tombs are rather less common here than the court tombs that characterise the west and north of the country. That makes the Prebaun example quietly notable simply by its type. The townland name itself, derived from the Irish, points to a landscape long settled and named by people who came well after the tomb's builders, generations for whom these massive stone structures were already ancient and perhaps already mysterious. The tomb would have stood in an open or lightly wooded Neolithic landscape, likely near cultivated ground, and has endured through every subsequent phase of land use in the area.