A faint rise in the ground, roughly 27 metres across, traced by a barely perceptible scarp, is what remains of a ringfort that stood here for centuries before being levelled around 1966. The site had been recorded on the Ordnance Survey Fair Plan map of 1837 as an oval enclosure, annotated simply as "fort", which was the common cartographic shorthand for these earthworks at the time. Within a few years of that levelling, it was, to the casual eye, gone.

Ringforts, sometimes called raths, were enclosed farmsteads typically dating from the early medieval period, defined by one or more circular earthen banks and ditches. They were built in their thousands across Ireland, and Balreagh sits in a cluster of them. Two further examples survive within a short distance of this spot, one approximately 150 metres to the north-west and another around 200 metres to the south-east, suggesting this hillock was once part of a densely settled agricultural landscape. The Balreagh fort occupied a commanding position, with open views to the north, east, and south, though higher ground rises to the south-west. What the Office of Public Works field report of March 1966 recorded as an act of levelling, aerial photography later quietly confirmed: a cropmark of the buried monument appeared in a Digital Globe image taken in November 2011, the circular outline reappearing as differential growth in the vegetation above the disturbed soil, a faint ghost of the original form pressing back through the ground.