That simple fact is what makes this field boundary in Ballynafullia worth pausing over. For a stretch of roughly twenty metres, the wall runs entirely beneath the surface of the peat, swallowed by centuries of accumulation, before re-emerging to continue its line across the hillside. In total, the visible and buried sections account for well over sixty metres of structure, with a short branch extending to the south-east at the south-western end and several upright stones set at right angles to the main line.

The wall itself is curvilinear, meaning it follows a gentle curve rather than a straight or geometric line, which is characteristic of pre-medieval field systems in Ireland, where boundaries tended to follow the natural contours of the land rather than any imposed grid. The surviving sections stand only around half a metre high and are roughly seven-tenths of a metre thick, reduced by collapse and time. What the bog has preserved, however, is arguably more informative than what remains above ground. Peat growth is slow and cumulative, and when a wall disappears beneath it, the bog effectively seals the structure at the point it was last in use or last maintained. The fact that this boundary runs under the bog suggests it predates the formation of that peat layer, potentially placing its construction in an era when the hillside supported a very different landscape, one open enough to require, or at least to reward, the effort of dividing it with stone.