What gives it an odd double life is the way its enclosing bank, built up to 1.7 metres high on the outside, has been pressed into service as an ordinary field fence along its northern, eastern, and southern sides. Farmers and archaeologists have, in effect, been sharing the same boundary for centuries without either party making much of a fuss about it.

The enclosure is a rath, the Irish term for a roughly circular earthen ringfort, the most common monument type in the Irish countryside. Thousands were built during the early medieval period, broadly the fifth to twelfth centuries, typically serving as enclosed farmsteads for a single family and their livestock. This one at Boolymore measures approximately 44.5 metres east to west and 38.8 metres north to south, making it a fairly standard example in terms of scale. Its bank is stone-faced on the exterior, which suggests rather more deliberate construction than a simple heap of thrown-up earth. Beneath the interior lies a souterrain, an underground stone-lined passage or chamber that served variously for storage, refuge, or ventilation of a dairy. The presence of one here signals that whoever lived within this enclosure invested real effort in the place, not merely marking territory but building infrastructure meant to last.