Ringforts, known in Irish as raths, are roughly circular or oval earthwork enclosures built primarily during the early medieval period, broadly between the fifth and twelfth centuries, and were typically the defended farmsteads of farming families. Thousands survive across Ireland in varying states of preservation, but the one at Castledown presents a particular case of compound damage: natural levelling, agricultural intrusion, and extensive quarrying have all taken their turn.

When the Ordnance Survey captured it on the revised 1913 edition of the 25-inch map, it was already recorded as a suboval earthwork, measuring roughly 47 metres across both its northwest-to-southeast and northeast-to-southwest axes. By the time a formal description was compiled in 1970, the picture was considerably bleaker. The northeastern half of the enclosure had been almost completely levelled. Where a bank still survives, running from the southeast around through south, west, and north, it has been reduced in places to little more than a scarp, a low slumped edge where an earthen wall once stood. The external fosse, the ditch that would have reinforced the bank's defensive profile, survives in partial traces only on the southern and western sides; elsewhere it has been obliterated, largely because the ground at the base of the bank has been badly damaged by quarrying. A large quarry hole sits within the western quadrant of the interior, and a modern bank and trench cut across the interior from southeast to northwest, curving westward, further complicating any reading of the original layout. No original entrance is recognisable. Despite all of this, the oval form remains legible in aerial photography, the earthwork still holding its shape against the surrounding fields even as its details have been eroded away over time.