A flat slab of limestone, modest in scale at roughly two thirds of a metre tall, carries a cross cut into its surface in three parallel incised lines, giving the Latin cross a quietly emphatic quality, as though the carver wanted the form to register without any flourish of relief sculpture or decorative fill. It is the kind of object easy to walk past, yet it belongs to a tradition of early medieval stone-working that shaped the visual culture of Ireland's monasteries for centuries.

Castledermot, known in early sources as Diseart Diarmata, the hermitage of Diarmait, was founded in the ninth century and grew into one of the more significant ecclesiastical sites in Leinster. The town still holds a remarkable concentration of early medieval stonework, including two high crosses and a Romanesque doorway, which makes the survival of a relatively plain incised cross-slab here entirely in keeping with the character of the place. Cross-slabs of this type, simple grave markers or boundary stones incised with a cross rather than carved in high relief, are common across early Christian Ireland and represent an older and less costly tradition than the freestanding high crosses for which sites like Castledermot became famous. The triple-line incision on this particular example gives the cross a defined weight without requiring the deep undercutting of more elaborate work. The limestone itself, measuring 0.34 metres wide and 0.10 metres thick, is a durable local material well suited to outdoor survival.