These earthworks, known in Irish as raths, were typically built during the early medieval period as enclosed farmsteads, their circular banks defining a protected living and working space for a family and their livestock. At Coolnahane, the enclosure measures roughly 30.5 metres east to west and 28.5 metres north to south, a modest but typical example of the form, now so reduced that it reads more as a gentle swell in the pasture than anything resembling a fortification.

When Bowman recorded the site in 1934, the single enclosing bank still stood at around four feet in height and the diameter was noted at approximately forty yards, on land belonging to a J. Fitzgerald. The 1842 Ordnance Survey six-inch map adds an intriguing detail: a limekiln is shown on the southern bank of the enclosure. Limekilns, used to burn limestone into quicklime for agricultural improvement and mortar, were a common feature of nineteenth-century Irish farmland, and their placement within or against older earthworks was not unusual; the ready-made bank offered convenient shelter and an existing elevated position. The coincidence of a prehistoric or early medieval boundary and a nineteenth-century industrial feature in the same spot says something about how these old earthworks continued to shape the working landscape long after their original purpose was forgotten. The site's bank is still detectable as a soilmark in aerial photography, suggesting that what has been lost above ground survives, at least in outline, below it.