This is a rath, the most common type of early medieval settlement in Ireland, typically consisting of a circular raised area defined by an earthen bank and ditch, the interior serving as a farmstead for a single family or small household. What survives in Grillagh Barony is a circular area some 36 metres across, east to west, its outline preserved in the subtle language of ground-level archaeology rather than in any dramatic masonry.

The defining feature is a scarp, that is, a natural or constructed slope in the earth, running from the north-northeast around to the west and standing to a height of roughly 0.9 metres. On the outer side, between the east-northeast and southeast arcs, a shallow depression still traces what was likely a surrounding ditch. Together, the scarp and depression form the classic signature of a rath, the bank thrown up from material excavated to create the enclosure ditch beside it. The interior has not escaped entirely intact; a field fence running northeast to southwest cuts across the northwestern portion, dividing what would once have been a unified enclosed space. This kind of truncation is common across Ireland, where centuries of agricultural boundary-making have quietly bisected ancient enclosures without anyone necessarily realising what lay beneath the fence posts.