Where the more familiar earthwork ringfort was thrown up from ditched soil and sod, the cashel relies on stacked stone, and in the rocky west of Ireland that material was rarely in short supply. These enclosures, most of them dating to the early medieval period roughly between the fifth and twelfth centuries, served as farmsteads for free farmers and minor lords, the circular wall defining both a domestic boundary and a statement of social standing.

Coolnafarna sits in a part of Mayo where the landscape itself carries the weight of long settlement. The cashel form is particularly associated with the stonier, more exposed ground of Connacht, where turf and timber were scarcer than limestone flags and field clearance produced ready-made building material. The word cashel derives from the Irish caiseal, itself borrowed from the Latin castellum, a small fort, though the domestic reality of most of these sites was considerably quieter than that military ancestry might suggest. Within the enclosing wall there would typically have been a house or houses, animal pens, and perhaps a souterrain, an underground stone-lined passage used for storage or refuge.

Because the formal record for this particular site has not yet been made publicly available, the finer details of its dimensions, condition, and any associated finds remain out of reach for now. What can be said is that cashels of this kind are frequently easier to read on the ground than earthwork forts, the stone walls sometimes still standing to a considerable height, and Coolnafarna is worth approaching slowly and on foot, allowing the enclosure's shape to resolve itself gradually from the surrounding field patterns.