Both editions of the OS record it clearly enough, the cartographers' lines preserving the outline of something that had been part of the landscape for centuries. But sometime in the 1950s it was levelled, and today there is no visible surface trace whatsoever.

Circular enclosures of this kind are among the most common archaeological features in the Irish countryside. They typically consist of an earthen bank and ditch enclosing a roughly circular area, and were used variously as farmsteads, places of assembly, or settlement sites across a broad sweep of Irish prehistory and the early medieval period. What makes Knocknaboola quietly melancholy is that its enclosure survived long enough to be mapped twice, but not long enough to survive the mid-twentieth century's appetite for agricultural improvement. The 1950s saw considerable land clearance across Ireland, and many such earthworks were removed by farmers using machinery that had not been available to earlier generations. The OS maps become, in such cases, the only remaining record of a feature that had stood for perhaps a thousand years or more.