This is a cashel, the Irish term for a stone-walled ringfort, a type of enclosed settlement built throughout early medieval Ireland, typically between the sixth and tenth centuries. Where timber ringforts used earthen banks and ditches, cashels relied on drystone construction, and thousands survive across the country in varying states of preservation. This one measures roughly 16.5 metres east to west and 14.6 metres north to south, modest even by the standards of its type.

The enclosure's builders accommodated the natural slope of Knockbrack in a practical way: the interior has been raised on the western side by about 1.6 metres, levelling the ground within the walls rather than fighting the gradient. The original drystone wall, which survives along the western, northern, and southern arcs, stands only about 0.3 metres high in most places, though it is roughly a metre thick. At some point a later stone field boundary was laid directly on top of it, reaching 1.5 metres in height, effectively borrowing the ancient structure as a ready-made foundation. This kind of reuse is common across rural Ireland, where farmers have long incorporated prehistoric and early medieval stonework into working field systems without any particular ceremony. A small rectangular field adjoining the north-eastern arc of the cashel appears on the Ordnance Survey six-inch map of 1895 and was still visible in aerial photography taken in 1973, suggesting the land around the enclosure has been managed and subdivided for at least a century and a half.