Whatever lay beneath the canopy was either unrecognised or quietly ignored, and so a substantial ringfort spent the better part of two centuries filed away, in cartographic terms at least, as forestry rather than archaeology.

A ringfort, sometimes called a rath, is one of the most common monument types in Ireland, typically a circular enclosure defined by a single earthen bank and ditch, used as a farmstead or defended homestead during the early medieval period. What makes this particular example at Carn unusual is its scale and its complexity. The enclosure measures approximately 53 metres east to west, which places it at the larger end of the spectrum, and it is defined not by one bank but by two earthen banks with an intervening fosse, the term for the ditch dug between them. The inner bank is wide and low; the outer has been partially levelled over time. The fosse itself is wide and deep, though quarrying activity has disturbed the north-eastern section. The whole monument sits on gently sloping grassland with open views to the south, on the demesne lands associated with Pakenham Hall, which lies roughly 890 metres to the south-east. A second ringfort stands about 260 metres to the east, suggesting this stretch of land was once more densely occupied than its present quiet appearance implies. Mature oak trees now grow along the perimeter of the earthworks, which may partly explain why earlier observers read the place as a plantation rather than a monument.