A two-metre slab of Old Red Sandstone rises from a low saddle of ground in County Waterford, its top coming to an oddly sharp point that almost certainly was not part of the original design. Somebody, at some point, appears to have tried to destroy it. The stone survived, but carries the marks of that encounter, as well as something considerably older: an ogham inscription cut into its angles.

Ogham is an early medieval script, typically found in Ireland and parts of Britain, in which letters are represented by groups of notches and strokes running along the edge or ridge of a stone. At Crehanagh, the inscription runs along the SE and SW angles of the monolith, which was itself an earlier standing stone, rectangular in cross-section and oriented north to south, before the ogham was added. The scholar R. A. S. Macalister, working in 1945, read the surviving text as VOCAGNI MAQI CUR(I)T, a formula broadly meaning "of Vocagnus, son of Curitus", a type of memorial or territorial marker common to the early centuries of the first millennium. A break near the top of the stone has probably cost the inscription its final letter or letters, most likely a closing vowel. Macalister also noted signs that an even earlier inscription may have been removed from the stone before the current one was carved, which raises the possibility that this particular block of sandstone has been reused and reinscribed across more than one generation, each act of writing overlaying or erasing what came before.