This is a rath, the most common type of early medieval enclosure in Ireland, typically built between roughly the fifth and twelfth centuries as a defended farmstead for a single family and their livestock. What makes the Greenhills example quietly notable is how much of it survives: at nearly fifty metres across, the enclosure is defined by two concentric earthen banks with a fosse, or ditch, running between them, a configuration that suggests the occupants either had significant resources or felt a genuine need for additional protection.

The layout follows a pattern seen across Ireland, where a raised inner bank enclosed a domestic area, while the outer bank and intervening ditch added a further layer of defence or status. At Greenhills, the inner bank has been worn away on the north-eastern arc, leaving that section without a visible surface trace, though the outer works remain. A gap on the southern side may represent the original entrance, a detail worth noting since original entrances to raths frequently faced east or south, orientations linked in early Irish sources to both practicality and convention. Whether that southern gap is genuinely ancient or a later breach is difficult to say without excavation, but its position is consistent with the broader pattern.