The enclosure measures just over thirty-seven metres across, which is a fairly typical diameter for this kind of monument, though the precision with which it has survived is quietly remarkable. A low earthen bank, roughly three metres wide and less than a metre high, traces the circuit, with a shallow external ditch, or fosse, running alongside it. The original entrance gap, four metres wide, faces east, which is the most common orientation for these structures in Ireland.

This is a rath, the Irish term for a ringfort, a class of monument that was built and occupied primarily during the early medieval period, roughly between the fifth and twelfth centuries. Raths were the enclosed farmsteads of their time, the bank and fosse serving less as serious military defences and more as a means of defining a household's space, keeping livestock in and wild animals or opportunistic raiders at least partly out. Tens of thousands of them once existed across Ireland, making them among the most numerous field monuments on the island. The Barnacleagh example is unexceptional in scale but notable for its condition. The survey recorded no visible internal features, meaning whatever structures once stood inside, whether timber buildings, a souterrain, or a hearth, have long since vanished beneath the surface or were never substantial enough to leave a lasting trace above ground. The gaps visible in the bank other than the eastern entrance are modern intrusions rather than original openings.