What the Ordnance Survey mapped in 1842 as a hachured circular enclosure of around 35 metres across had, by the time later surveyors visited on foot, been reduced to a circular area of just 22.5 metres, defined by two low concentric rises with a shallow depression running between them. It survives in tillage, which goes some way towards explaining the attrition.

A ringfort, or rath, is one of the most common monument types in the Irish landscape: a roughly circular enclosure defined by an earthen bank and ditch, typically dating to the early medieval period and associated with a single farmstead or small settlement. At Killowen, the Ordnance Survey's six-inch maps provide a kind of time-lapse record of what has been lost. The 1842 map shows the enclosure with hachuring, the standard cartographic shorthand for a raised earthwork with discernible slope. The 1904 revision records it still, presumably in recognisable form. By 1937, the language of the mapping had shifted: the feature is described only as a raised circular area, suggesting the defining bank had by then been substantially reduced. What remained when surveyors later examined the ground was the ghost of a structure rather than the structure itself, two faint concentric swellings in the earth and a slight hollow between them.