It measures roughly 1.77 metres by 1.2 metres, and across its face runs an unusual interlocking pattern of four saltires, the diagonal X-form crosses familiar from heraldry and early Christian stonework, each rendered in triple incised lines with circular centres and terminations. What makes the design genuinely uncommon is the way these four crosses are arranged to form a single continuous pattern covering the whole surface rather than sitting as isolated motifs. Whether the slab originally served as a tomb cover or as an altar frontal, a decorative facing placed at the front of an altar, remains unresolved, though the latter use has been considered quite plausible.

The slab's history adds another layer of uncertainty. It is said to have been brought to its present location from Reefert Church, one of the cluster of early medieval ecclesiastical sites scattered through the Glendalough valley. Reefert, whose name derives from the Irish for "royal burial place", sits further up the valley near the upper lake, and its association with the slab suggests the stone may have had a significant liturgical or funerary role in that community before being moved. Harold Leask, writing in 1950 in his guide to the national monuments at Glendalough, was the source of the detailed description that draws attention to the design's rarity. A second cross-slab is also visible nearby, suggesting the church once held a small concentration of carved stonework that has not always received the individual attention each piece might warrant.