What looks at first glance like a natural swelling in the field turns out to be a carefully defined circular enclosure, roughly 18 metres from north to south and 16.5 metres from east to west, its edge marked by a scarp dropping about 1.5 metres on the outside and a modest internal lip running north to south on the inner face. The slight asymmetry between those two measurements, and the deliberate shaping of that inner edge, suggest human intention rather than geology.

Enclosures of this kind are among the more quietly persistent features of the Irish landscape. The term covers a broad range of circular or near-circular earthworks, from ringforts used as defended farmsteads in the early medieval period to earlier ceremonial or boundary structures whose purposes remain harder to pin down. The raised, scarped form at Greenane fits within that tradition, though without excavation it is difficult to assign it a precise function or date. What complicates the picture further is that the south-western arc of the interior has been absorbed into a later field boundary, meaning the enclosure has been partially overwritten by agricultural activity at some point in its long afterlife. That kind of incremental reuse is common across Ireland, where earlier earthworks were pressed into service as convenient walls or boundaries by successive generations of farmers who may or may not have known what they were working with.