It belongs to a category of site known only through cropmarks, where buried archaeological features alter the growth rate of overlying crops or grass, producing faint colour and texture differences that reveal themselves only under the right light and at the right season.

What survives at Lisduggan is the cropmark of a fosse, the defensive or boundary ditch that once ringed a circular enclosure roughly thirty metres in diameter. Enclosures of this kind are widespread across Ireland and typically associated with early medieval settlement, the fosse defining the limits of a farmstead or small community. At Lisduggan, a field fence and a road have clipped the north-western edge of the circle, erasing part of the original circuit. The site came to light in July 1989 through aerial photography carried out as part of the Cork Aerial Survey and Archaeological Photography programme. In the same photographs, additional linear cropmarks were noted to the south and east of the enclosure, suggesting further buried features in the surrounding land, though their precise nature remains unresolved.

There is nothing to see at ground level. The value of Lisduggan lies precisely in that absence, in the way it demonstrates how much of early Irish settlement has vanished from the surface while remaining, faintly and precariously, just beneath it.