It is modest in scale, roughly nine metres by eleven, and it would have remained entirely invisible had it not been disturbed during an afforestation project. What emerged was a burnt layer sitting only a matter of centimetres underground, the stones within it shattered by repeated exposure to intense heat.

This is a burnt mound, a type of site found widely across Ireland and Britain, typically dating to the Bronze Age, though some examples span into the Iron Age. The leading interpretation is that they functioned as cooking places, where stones were heated in a fire and then dropped into a water-filled trough to bring it rapidly to the boil. The repeated heating and sudden cooling causes the stones to fracture in a characteristic way, and over time the discarded, heat-shattered fragments accumulate into a mound alongside the darkened, charcoal-rich soil that gives these sites their name. The example at Aghnagarron, in County Longford, came to light during monitoring work, when Richard Crumlish recorded the burnt layer lying just beneath the peat, the shattered stones ranging from around thirty to one hundred and thirty millimetres in size.