The ringfort at Monkstown is a rath, the most common type of early medieval enclosure in Ireland, typically a circular area defined by one or more earthen banks and a surrounding ditch, used as a farmstead or defended homestead. This one spans roughly twenty metres across its northeast to southwest axis, its bank now poorly preserved and its external fosse, the shallow defensive ditch outside the bank, only faintly legible at the northeast and southwest edges. A field fence cuts across the perimeter at the southeast, a mundane agricultural intrusion that has done its own quiet damage over time.

What makes this site particularly interesting is how the historical record catches it in the act of being misread, or perhaps simplified, across the decades. The first edition Ordnance Survey six-inch map of 1837 depicts it as a bivallate ringfort, meaning one with two concentric banks and ditches, suggesting a more substantial and possibly higher-status enclosure than a single-ringed farmstead. By the time the revised twenty-five-inch OS map was produced in 1911, only a single bank was recorded, and the field boundary cutting through the southeast was already marked as a nineteenth-century feature. Whether the outer bank had genuinely disappeared in those intervening decades through agricultural clearance or gradual erosion, or whether the earlier surveyor was simply more attentive to faint earthworks in the field, is now difficult to say with certainty. By November 2011, aerial photography showed the site covered in trees, adding another layer of concealment to a monument already working hard to remain invisible.