It is not. What survives here is a rath, the commonest monument type in the Irish countryside, a ringfort built during the early medieval period, roughly between the fifth and twelfth centuries, and used primarily as an enclosed farmstead for a family of some local standing.

The earthwork at Cartronabree is oval in plan, with an interior diameter of around 31 metres, enclosed by a horseshoe-shaped bank roughly five metres wide and surviving to a height of about 0.60 metres. That horseshoe shape is worth noting. A complete circuit of bank and ditch is the expected form, so the open end here suggests either that the enclosure was never finished on one side, or more likely that centuries of agricultural activity have worn away what once closed the ring. There is only the slightest trace of a ditch, which would originally have sat outside the bank and provided the material for it. In its working life, the raised interior would have held a house or houses, perhaps outbuildings, and the whole thing would have presented a more imposing barrier than what the present modest earthwork implies.