Beneath and beside it, an arc of drystone masonry curves from south-east to south, all that is left of a circular enclosure that once measured roughly 25 metres across. The field wall was built later, enclosing the monument entirely, and in doing so both preserved and obscured it. Dense overgrowth has since finished the job, making the site effectively inaccessible to anyone who might want to look closely.

Circular enclosures of this kind are a common enough feature of the Irish archaeological landscape, though their precise function varies. Some were ringforts, the enclosed homesteads of early medieval farmers, defined by an earthen bank or a drystone wall called a cashel. Others served as burial grounds, stock enclosures, or the defended bases of local lords. Without excavation it is rarely possible to say which category applies, and Keernaun offers no exception. What can be said is that the site was significant enough to be recorded on the Ordnance Survey six-inch maps, those meticulous nineteenth-century surveys that captured the Irish countryside before so much of it changed, and that the circular form was still legible enough at the time of mapping to be noted and measured.