At its centre is a shallow depression, and that detail, modest as it sounds, is the giveaway. This is a fulacht fia, a type of prehistoric cooking site found in enormous numbers across Ireland, and the depression marks where a water trough once sat, filled and reheated by dropping fire-cracked stones into it until the water boiled. The discarded stones, fractured by repeated heating and cooling, gradually built up around the trough into the horseshoe or oval mound that survives today.

Fulachtaí fia are among the most common archaeological monuments in Ireland, yet individually they are easy to overlook, especially when they sit quietly in farmland that has been worked and rewrked for generations. The one at Rathnagard measures sixteen metres on its longer north-east to south-west axis and nine metres across, making it a reasonably substantial example. The burnt mound material that forms its bulk is the accumulated waste of what may have been many episodes of use, most likely during the Bronze Age, though the sites as a class span a considerable period. The reclaimed pasture setting hints at how thoroughly the surrounding landscape has been altered since the mound was left, while the mound itself, protected partly by its own bulk, has remained largely intact.