It measures roughly 23 centimetres high and 30 centimetres wide, with only about 5 centimetres of thickness visible where it sits flush against the wall. What makes it worth pausing over is what is carved onto its face: an incised outline Latin cross with expanded terminals, the arms flaring slightly at their ends in a style common to early medieval Irish stonework, and below the cross, a single complete horizontal line of text. The lower edge of the slab has been damaged, but the inscription itself appears intact.

The stone was not always visible. It came to light during an excavation in 1944, documented by Duignan and later referenced by Macalister in 1949, and was subsequently set into the church wall where it has remained since. Scholars Okasha and Forsyth, writing in 2001, catalogued it as Toureen Peacaun 19 in their study of inscribed stones, noting its modest dimensions and the apparent completeness of the slab despite the edge damage. Cross-slabs of this type, flat stones incised with a cross and sometimes an accompanying inscription, were a common form of early Christian memorial or dedicatory marker in Ireland, used from roughly the seventh century onwards to mark graves or commemorate individuals, often in monastic contexts. St Peakaun's itself is an early ecclesiastical site, which makes the presence of such a piece entirely in keeping with the layered history that tends to accumulate at these places.