The earthwork itself is gone, levelled long ago by farming, but its outline can still be read from the air: a roughly circular cropmark, approximately thirty metres across, tracing what was once a raised bank and fosse, the external ditch that typically surrounded these early medieval farmsteads. A ringfort, or rath, was the standard enclosed settlement of rural Ireland from roughly the fifth to the twelfth century, a small defended homestead for a farming family of some local standing. This one at Knocknacolan is invisible at ground level, yet its circular logic persists just beneath the surface.

The cropmark was captured in an aerial photograph taken in July 1989 as part of a Cork Archaeological Survey aerial programme. What the photograph revealed was not one trace but two: the faint ring of the enclosure itself, and cutting straight across it, the cropmark of a levelled field fence running roughly northwest to southeast. That fence postdates the ringfort, evidence of later agricultural reorganisation that eventually erased both features above ground. The enclosure is also set slightly off centre to the southwest within its own form, a small irregularity that might point to later modification or simply to the pragmatic asymmetry of early construction. A second ringfort lies approximately thirty metres to the northwest, suggesting that this part of Knocknacolan once held a modest cluster of enclosed settlements, a pattern not uncommon in early medieval Cork.