The enclosure at Ballyleen is a rath, the Irish term for a ringfort, which was the most common form of rural settlement in early medieval Ireland. Typically used as a farmstead by a single family and their livestock, these structures were defined by one or more earthen banks, sometimes topped with a timber palisade, enclosing a living and working area within. What makes this particular example quietly compelling is how well the ground still holds its shape.

The enclosure measures roughly 45 metres east to west and 44 metres north to south, making it nearly but not quite circular. Around part of the perimeter, from the south-east round to the south and continuing from the south-south-west to the north-west, a raised bank still marks the boundary clearly. Elsewhere, the edge survives as a scarp, a cut or slope in the ground rather than a built-up bank, which suggests either that the bank eroded away on those sides or that the original construction varied around the circuit. A band of noticeably darker vegetation running from the west to the north-west may mark the course of a fosse, an external ditch that would originally have run outside the bank, deepening the defensive or boundary effect of the whole enclosure. The vegetation difference, caused by soil disturbance or moisture retention in the old ditch line, is the kind of detail that reveals itself slowly to anyone walking the perimeter.