It once formed part of a remarkable cluster of fifteen ogham stones, the early medieval Irish script that uses a series of notches and lines cut along a central stem to record names and lineages, which had been repurposed, flat side down, as the roof lining of a souterrain, an underground stone-built passage typically associated with an Early Christian period settlement. The stones were not marking a burial or a boundary in the usual sense; they were doing structural work, holding up the dark.

The stones came to wider attention when the Reverend E. Barry lifted and recorded them in the nineteenth century, before replacing them. At some later point the occupiers of the land raised thirteen of the stones themselves; twelve of those are now on permanent display in the Stone Corridor at University College Cork, where they represent one of the most significant collections of ogham epigraphy in the country. The fifteenth stone, the one Barry had read and replaced, was simply too heavy to shift a second time. It remains in the ground, invisible, with no surface trace. Barry's reading of its inscription, later corrected by the scholar John Rhys, was ERACOBI MAQI ERAQETAI, a formula meaning roughly "of Eracobus, son of Eraqetas", the kind of genealogical declaration found on hundreds of ogham stones across Munster and Wales. The correction Rhys supplied was recorded by R.A.S. Macalister in his 1945 corpus of Irish ogham inscriptions.

For anyone curious enough to visit, the twelve surviving Ballyknock stones can be examined at close range in the Stone Corridor at UCC, where the inscriptions are legible and the stones are well presented. The one that stayed behind in Cork is a different matter entirely; its precise location on the ground carries no marker, and the inscription it bears exists now only in nineteenth-century scholarship.