Ogham is an early medieval script in which letters are represented by notches and strokes cut along the edge of a stone, typically used to record personal names and lineage in the Irish language. Finding one such stone is noteworthy; finding three in the same underground passage is the kind of thing that makes you wonder how they got there and why.

The stone in question is relatively modest in size, measuring just over three feet in length and roughly a foot wide, according to R.A.S. Macalister's 1945 catalogue. What survives of its inscription reads COIMAGNI MAQI MOCOI GA, a formula typical of early ogham texts, giving a personal name followed by a patronymic construction meaning roughly "son of" and a tribal or kindred designation. The inscription is incomplete, the ending lost, which leaves the full genealogical claim unresolved. A souterrain, for context, is a stone-lined underground passage or chamber, commonly associated with early medieval settlement sites in Ireland and thought to have served for storage or refuge. That three inscribed stones ended up inside one is curious; they may have been reused as building material, their original commemorative purpose long forgotten by whoever constructed the passage. The stone has since been removed and is now held in the National Museum of Ireland. It has also been digitally recorded as part of the Ogham in 3D project run by the School of Celtic Studies at the Dublin Institute for Advanced Studies, which has produced detailed three-dimensional scans of ogham stones across the country.