Sometime in the early medieval period, a stone already centuries old and carved with one of Ireland's oldest scripts was pulled from wherever it stood and repurposed as a roof slab for an underground passage. That secondary life, humble and structural, is how this ogham stone at Windgap in County Waterford survived at all.

Ogham is an early medieval script, used roughly from the fourth to the seventh centuries, in which letters are represented by groups of notches and strokes cut along the edge of a stone. The Windgap stone is a slate slab measuring 1.37 by 0.42 by 0.15 metres, and it served as a lintel in a souterrain, an underground stone-lined passage or chamber typically associated with a rath, the circular earthwork enclosure that was the standard farmstead of early medieval Ireland. The inscription was read by the scholar R. A. S. Macalister in 1945 as MODDAGN[I] MAQI GATTAGN[I] MUCOI LUGNI, a formula characteristic of ogham monuments: the name of the commemorated person, their father's name introduced by the word for "son of", and a tribal or kin-group designation. Translated loosely, it announces that this was the stone of Moddagnas, son of Gatttagnas, of the people of Lugnus. A second ogham stone was also used in the same souterrain, though that one has since been lost entirely.

What makes the survival of this stone quietly remarkable is its trajectory: carved as a memorial or marker, then absorbed into the architecture of a rath, its inscription facing inward for centuries while the earthwork above it continued in use. The displaced lintel, separated now from its original souterrain context, carries a personal name that would otherwise have vanished without trace.