A place called Black Rath might seem to announce itself clearly enough, but the earthwork that gave this corner of County Kildare its name is doing its best to disappear back into the ground. Sitting midway along a gentle slope that faces south-west, the site is a ringfort, one of the tens of thousands of circular enclosed settlements built across Ireland during the early medieval period, typically between roughly 500 and 1000 AD. Most ringforts consist of a bank, a ditch, and an interior where a family or small community once lived. Black Rath is no exception in type, but its condition is notably poor, the banks heavily worn down and the ground churned up by livestock over what must be many generations.

What survives is still legible to a careful eye. The interior measures just over twenty-one metres across, ringed by a wide earthen bank that in places originally stood more than two metres above the base of the outer fosse, the ditch that runs around it. A second, outer bank adds an extra defensive or enclosing circuit, making this a bivallate example, meaning it had two concentric banks rather than the single ring more commonly encountered. That outer bank, now only about thirty centimetres high at its best-preserved points, suggests the site was once considered worth the considerable extra labour of construction. A gap of roughly three metres in the inner bank on the north-east side is thought to mark the original entrance, though any causeway that would once have allowed passage across the fosse has been completely obscured by the same livestock poaching that has degraded the rest of the site. The interior, for its part, is now dense with nettles and thistles, the kind of vigorous growth that tends to colonise long-disturbed ground rich in nutrients.