The earthworks at Rathnacally have been levelled, leaving little more than a faint trace of the surrounding fosse visible at ground level along the eastern to south-western arc, but aerial photographs reveal the full geometry of what was once a substantial enclosure, its banks and ditches preserved as cropmarks, the differential growth of grass and grain betraying what centuries of ploughing could not quite erase.

Ringforts, known in Irish as raths, were the most common form of rural settlement in early medieval Ireland, typically the enclosed farmsteads of farming families built between roughly the fifth and twelfth centuries. They usually consist of one or more earthen banks, each accompanied by an outer ditch or fosse. The Rathnacally example was a bivallate enclosure, meaning it had two such banks with an intervening fosse and an additional external fosse beyond that, a configuration associated with households of somewhat higher social standing. What makes its history unusually legible is the sequence of Ordnance Survey maps that document its steady shrinkage over nearly a century. The 1842 six-inch map shows a nearly circular enclosure measuring around 100 metres east-to-west and 90 metres north-to-south. By 1905, the recorded diameter had reduced to roughly 80 metres, and by 1936 the mapped area had contracted again to approximately 70 by 60 metres, the fosse still shown but the structure clearly diminishing. Aerial photography by Dr D.D.C. Pochin Mould later caught the shadow site in oblique light, and a separate aerial photograph in the Geological Survey of Ireland collection shows the cropmark of the double-bank plan in plan view, the full bivallate layout restored, at least in outline, from above.