It is a rath, the Irish term for a ringfort, which is to say a roughly circular enclosure defined by an earthen bank and ditch, once used as a farmstead and domestic enclosure during the early medieval period. Thousands of these survive across Ireland, though many have been levelled by agriculture; what makes this one worth a second look is the detail accumulated around it across two centuries of mapping and observation.

The Ordnance Survey's six-inch map of 1840 recorded the feature as a raised, oval-shaped area, and by the time the twenty-five-inch edition appeared in 1897 it was described more precisely: a circular platform roughly thirty metres in diameter, defined by a scarp, a fosse (that is, a ditch), and an outer bank running from the south-west around to the north and south-east. The surveyors of 1840 also noted, in their field notebooks covering the territory from Abbeyfeale to Bruree, that the townland of Cloonbrien contained two ancient forts: one in the north, called Lisheengorm, and one in the south. This site is understood to be Lisheengorm, the northern of the pair. A second enclosure recorded in the area lies roughly 225 metres to the south-east, suggesting the two features may once have formed part of a broader pattern of early settlement across this stretch of farmland.

The fort sits in improved pasture about 130 metres north of a watercourse that marks the boundary between Cloonbrien and the neighbouring townland of Clogher West. A farm track running east to west passes immediately to its north, which provides a useful orientation point for anyone approaching from the road. By the time aerial photography was taken between 2005 and 2012, the circular form was still clearly visible, defined by a ring of trees growing along its perimeter, a common indicator of surviving earthworks in the Irish countryside where trees are left undisturbed on features that farmers have long learned not to plough. Later Google Earth imagery from September 2020 confirms the outline remains intact. The trees, as much as the earthwork beneath them, are what to look for.