It is the base of a cross, not the cross itself, and its modest dimensions, roughly 23 centimetres high and tapering from 37 centimetres wide at the base to 28 centimetres at the top, give little immediate indication of what it once held. Cut into its upper surface is a rectangular socket, the void where the shaft of a now-missing cross would have been set. Faint incised decoration survives on all four faces, though the stone has clearly had a long and displaced life.

The scholar R.A.S. Macalister first recorded this fragment in 1916 to 1917, noting it at the north wall of the nave of St. Caimin's church, one of several early medieval ecclesiastical structures clustered on this small island in the lower Shannon. St. Caimin's is associated with the seventh-century saint of the same name, and Inis Cealtra, sometimes anglicised as Holy Island, was a significant monastic site throughout the early Christian period. The cross base has since been moved inside for protection, which is how an object recorded against a church wall a century ago ends up housed in a modern building on the same island. The socket itself is a useful reminder of how these monuments worked: the shaft and head of a standing cross were often separate pieces of stone, slotted together, and when the upper section is lost or removed, the base can look almost purposeless to an unprepared eye.