The site is a fulacht fia, a type of monument found in considerable numbers across Ireland, typically consisting of a horseshoe-shaped mound of fire-cracked stones beside a trough and a hearth. They were used to heat water by dropping stones made red-hot in a fire into the trough, most likely for cooking, though theories about their use for brewing, bathing, and textile processing have all been put forward by archaeologists. The Mullenroe example, however, offers none of that familiar mounded silhouette. It was levelled during drainage or land reclamation work, and no visible surface trace remains.

The loss is not unusual. Land drainage and agricultural improvement, carried out across Irish farmland from the eighteenth century onwards and intensifying through much of the twentieth, disturbed or destroyed a significant proportion of low-lying archaeological features. Fulachtaí fia are particularly vulnerable because they tend to occupy wet, marginal ground close to streams or boggy hollows, precisely the kind of terrain targeted for reclamation. The site at Mullenroe survives in the record rather than in the landscape, its existence documented before whatever machinery or drainage scheme removed the last trace of it from the surface of the field.