That ambiguity is part of what makes it interesting. Most defended medieval towns in Ireland received murage grants, royal licences that permitted the levying of tolls on goods entering the town in order to fund the building of walls. Clonmines received no such grant, which leaves open the question of whether it was ever formally defended at all.

What survives is a field bank roughly two metres wide and two metres high, with a flat-bottomed fosse, or ditch, cut along its eastern side. The ditch runs about four metres across and drops to around a metre in depth. Together, the bank and fosse extend approximately 200 metres northward from the graveyard where the town's fortified church and St. Nicholas' parish church still stand, following a line that would have closed off the settlement at a bend in the east-west course of the Owenduff river, some 500 metres north of those churches. The town itself sits on a gentle slope tilting northward and eastward toward the Owenduff/Corock river, around 300 to 350 metres to the east. The topography, in other words, was doing some of the defensive work already, and this earthwork may have been intended to close the one side that natural features left exposed. Whether it represents a deliberate, if informal, town boundary, a property division, or something more defensive in intent remains an open question.