It is easy to overlook, being just over a metre and a half tall and barely a palm's width across, but the marks carved along one of its edges place it in a tradition of writing that predates the Norman arrival in Ireland by many centuries. This is an ogham stone, inscribed in an early medieval script in which letters are represented by notches and strokes cut along a central stemline, typically along the edge of a standing stone.

The stone was found not within the cathedral precinct but in a field across from where a Protestant church once stood nearby. How it came to rest there, and what journey it made before being moved into the cathedral for safekeeping, is unrecorded. The inscription itself is only partially legible, the stone having been badly damaged at some point before it was properly studied. The surviving letters, as transcribed by R.A.S. Macalister in his 1945 corpus of ogham inscriptions, read something like 'CT[A(?)]N' on one line and 'QLOG' on another, with further characters either lost or indeterminate. Whether these fragments once formed a personal name, a memorial formula, or something else entirely remains uncertain. The stone has since been examined as part of the Ogham in 3D project run by the School of Celtic Studies at the Dublin Institute for Advanced Studies, which uses digital scanning to capture inscription details that the naked eye can miss on worn or fragmented examples.