This is a rath, the Irish term for a ringfort, the kind of enclosed farmstead that was built in its thousands across Ireland during the early medieval period, typically between the fifth and twelfth centuries. What makes the one at Kilrusheighter quietly interesting is how little conventional construction it actually required. Analysis of aerial photography suggests the enclosure was originally circular, roughly thirty metres in diameter, but its builders were pragmatic: along the northern, north-eastern, and south-western sides, the natural slope of the ridge served as the boundary itself, doing the work that a constructed bank would otherwise have had to do.

Only on the western side, where the ridge face is at its highest and steepest, reaching approximately four and a half metres, did the builders add a deliberate linear bank and gully running north-east to south-west. This is the one point where the topography alone was evidently not considered sufficient to close off the enclosure. More intriguing still, at the south-western end of this bank, close to the edge of the ridge, the earthwork appears to cut through the remains of what may be an earlier hut site. If that reading is correct, the bank was constructed after the hut, and something of an earlier phase of occupation lies partly buried beneath it, the sequence of use at this spot extending back further than the ringfort itself.