A rath, as this type of enclosure is known in Irish, was typically a circular earthwork enclosure used as a farmstead during the early medieval period, defined by one or more earthen banks and ditches. This one measured roughly 30 metres in diameter, and the only documentary evidence of its shape comes from the Ordnance Survey six-inch map of 1842, which recorded it as a clearly defined circular enclosure. Since then, agricultural levelling has removed every visible trace. The field carries on, indifferent to what lies beneath it.

What makes Barnabrow quietly interesting is not the absence of this particular fort, but the company it once kept. Two further circular enclosures survive to the north-east, one approximately 120 metres away and another around 260 metres beyond that. Groups of ringforts appearing within close proximity of one another are not unusual in the Cork landscape; they may represent successive generations of the same family farming adjacent plots, or related households occupying the same territory over centuries. The Barnabrow fort, had it survived, would have formed part of that cluster. Instead it exists only as a map annotation and a scheduled record, a placeholder for something the plough has long since erased.