That kind of pragmatic accommodation is not unusual in early medieval Ireland, but it gives the site at Carrigonirtane an oddly fractured quality, the enclosed space divided by geology before anyone ever raised a wall.

The fort sits atop a natural rise among rough grazing ground, a position typical of the rath tradition. A rath is an early medieval farmstead enclosure, usually dating from roughly the fifth to the twelfth century, defined by one or more earthen banks and ditches rather than stone walls. Here the roughly circular enclosure measures about 25 metres east to west and 23 metres north to south. Its earthen bank still stands to an internal height of 1.4 metres, and in places the inner face of that bank is reinforced with stone, a detail that points to some care in the original construction. Outside the bank, a fosse, meaning a ditch dug to enhance the defensive effect of the bank, survives along the northern to south-eastern arc, reaching a maximum depth of 0.8 metres. The entrance, 2 metres wide, faces the south-south-east, and a causeway carries the threshold across the fosse. A secondary gap opens to the north-north-east, though whether this was always an intentional opening is less clear. A short distance to the south-east lies a stone row, a separate prehistoric monument that predates the fort by potentially thousands of years, lending the immediate landscape an unusual density of human marking across very different periods.