The earthwork itself is straightforward enough, a roughly circular enclosure about fifty metres across, sitting on a north-facing slope in pasture at Knocknacolan. But the old map records a second bank curving concentrically around the northern and eastern sides, and then continuing southward beyond the enclosure before bending back in the opposite direction. That reversal is the puzzling detail. Rather than completing a neat outer ring, the feature doubles back on itself, suggesting either a more complex original design or a later alteration whose purpose is no longer obvious from the ground.

Ringforts, known in Irish as raths when built from earth, were the most common settlement type in early medieval Ireland, typically dating from roughly the sixth to the twelfth centuries. A farming family would have lived inside the enclosed area, using the bank and its accompanying external ditch, or fosse, to define their space and offer a degree of protection for people and livestock. At Knocknacolan, the builders had to contend with the gradient of the hillslope, raising the interior on the northern side to create a level living surface. The bank itself is considerably more imposing on the outside than within, standing nearly 1.9 metres on the exterior face against just 0.42 metres internally. Three breaks in the bank, to the south-south-east, south-south-west, and north-north-west, may represent original entrances or later gaps. The fosse has largely flattened to a gentle slope rather than a true ditch, which is common on sites that have been under agricultural use for centuries.