They mark the roof of a souterrain, an underground stone-lined passage or chamber built during the early medieval period, typically used for storage or refuge. Most of what lies beneath is hidden, and at the time it was last examined, the structure was blocked and could not be entered. The visible stones are, in a sense, all that announces it.

The souterrain sits in the south-western part of a ringfort, the circular earthwork enclosure it once served. Ringforts were the most common form of rural settlement in early medieval Ireland, and souterrains were frequently built within them, their entrances often concealed and their passages deliberately narrow. The Carrowreaghmony example was recorded in a 1994 archaeological survey of the Ballinrobe district compiled by D. Lavelle, which placed it in the broader landscape around Lough Mask and Lough Carra in County Mayo. Beyond the three protruding lintels and the note of inaccessibility, the survey offers little further detail, which is itself quietly telling: some sites are known mainly by the fact of their concealment.