The cross-slab at Reachlainn Uí Bhirn, catalogued as DG089-018003, is a small, roughly hewn monument measuring just 66 centimetres tall and 30 centimetres wide. Its thickness varies between 4 and 5 centimetres, and it tapers to a slightly gabled apex that sits off-centre, giving the stone an endearingly imperfect character.

Both faces of the slab bear simple incised crosses near the top, though time and weather have taken their toll. The cross on Face A, carved in shallow lines, stretches 17 centimetres high and 21 centimetres across the arms. It's a plain, crudely formed design with just a hint of rounded broadening at the upper and right terminals. Face B tells a more melancholic story; the stone surface has scaled away near the apex, destroying the upper portion of its cross. What remains measures 20.2 centimetres across the transom with a lower limb of 11.3 centimetres, suggesting it once mirrored the simple style of its counterpart.

These crosses, whilst lacking the elaborate artistry found on more famous Irish high crosses, represent the grassroots tradition of Christian marking in medieval Ireland. The slab was documented by archaeologist Michael Herity in 1995 and earlier by Paul Walsh in 1983, who noted the subtle rounded expansions on the cross terminals; small details that hint at the maker's attempt to add a touch of refinement to this otherwise humble memorial.