It is not especially large, measuring 1.72 metres in total length, and it does not announce itself with inscription or figural carving. What it offers instead is something more quietly cryptic: a set of six incised lines radiating outward from the centre of the stone, semi-circular loops running along both sides and the narrow end, and, at the broad end, two cupmarks sitting either side of a central line. The overall effect is almost diagrammatic, a kind of abstract geometry pressed into local granite by someone who understood exactly what they were doing, even if the reasoning behind each element is no longer recoverable.

This is a Rathdown-type grave slab, a category of early medieval monument found predominantly in the Dublin and Wicklow region. The type is named for the historic barony of Rathdown, and the decorative conventions, those radiating lines, the looped borders, the cupmarks, recur across the group with enough consistency to suggest a shared tradition of funerary craft. The Rathfarnham example has been dated by researchers to somewhere between the 9th and 12th centuries, placing it in the period after the Viking settlements but before the Anglo-Norman reorganisation of Irish ecclesiastical life. It was documented by Breen in 1981 and later included in a 2009 edited volume by K. Swords, with the site record compiled by archaeologist Geraldine Stout.

The slab sits in the churchyard at Rathfarnham, to the north-east of the church building itself. Visitors should be aware that it is broken into two pieces, so it requires a moment of visual assembly to read it as a whole. The incised decoration is on one face only, and depending on the light, the lines can be easier or harder to make out; overcast conditions, which flatten shadows rather than deepen them, can sometimes make shallow incisions on stone harder to read than low-angle sunlight would. The cupmarks at the broad end are worth particular attention, small circular depressions that belong to a tradition reaching back far earlier than the slab itself, though their specific meaning in this context remains a matter of scholarly discussion rather than settled fact.