What they are crossing, however, is the perimeter of an ancient enclosure, a monument that has survived in the landscape of Castle-Erkin South through no more dramatic means than the slow accumulation of earth and the reluctance of farmers to plough over inconvenient humps. Its survival is quiet and almost accidental, which makes it all the more worth paying attention to.

The enclosure was recorded and compiled by Denis Power, with details uploaded in June 2013. It sits on a south-east-facing slope, positioned to catch the morning light and offering open views across the countryside from north-east to south-west. The monument measures roughly 20.5 metres on its north-west to south-east axis and 17.5 metres across from south-west to north-east, making it a modest but clearly defined feature. What gives it its shape on the ground is a scarped edge, that is, a deliberately cut or shaped bank of earth, running to a width of around five metres and standing to a height of approximately 2.3 metres in places. On the outer side, from the north-west around to the north-east, there is a fosse, a shallow external ditch, roughly 4.2 metres wide and half a metre deep. The interior of the enclosure slopes gently downward toward the south-east. Enclosures of this general type are found throughout Ireland and are often associated with early medieval settlement, though without excavation it is difficult to assign this one a firm date or function.

The site lies in open farmland and, as with many such monuments in County Limerick, access will depend on the goodwill of the landowner and the condition of the ground underfoot. The scarped bank is the most legible feature from within the enclosure itself, and the external fosse, though shallow, is easier to read when the vegetation is low in late winter or early spring. Standing inside and looking south-east down the slope gives a sense of why this particular spot was chosen, sheltered at the back, open to the view ahead, the same practical logic that has guided settlement in Ireland for millennia.