A rath, roughly speaking, is a circular earthen enclosure, typically dating from the early medieval period and associated with a farmstead or small settlement, defined by a raised bank and sometimes an outer ditch. The one at Castlehill was never a dramatic monument, but by 1838, when the first Ordnance Survey six-inch maps were made, it registered clearly enough as a circular feature approximately forty metres in diameter. A field boundary running northeast to southwest bisected it to the north of its centre, which was already a bad sign. By the 1922 edition of the same map, surveyors could only make out the northwest third, rendered in the hachured shorthand that cartographers used for earthwork remains. The rest had gone.

The site has since been levelled, folded into the surrounding pasture on low ground that falls gently eastward toward flat, somewhat wet terrain. What survives now is an oblong rise, measuring roughly sixteen metres northwest to southeast and perhaps twenty-five to thirty metres in the other direction, faintly defined along its northwest arc by a slight scarp. A scarp here is simply an abrupt change in slope, just enough to suggest where the original bank once ran. Further south, faint undulations hint at the enclosure's former extent, but the full circular outline can no longer be read from the ground. A second possible rath sits around 140 metres to the north, which suggests this part of Castlehill once had some concentration of early settlement activity, even if almost nothing of either site is now legible.