Among the four bullaun stones at Crough in County Waterford, one never quite made it to whatever purpose its maker intended. A bullaun is a stone, often associated with early Christian or pre-Christian sacred sites, that has been deliberately hollowed to produce one or more rounded basins; the basins were used for grinding, for collecting rainwater thought to have curative properties, or possibly for liturgical purposes. Three of the Crough stones, all of coarse conglomerate, carry one, two, and three basins respectively, suggesting deliberate accumulation or incremental working of the material over time. The fourth is different: sub-triangular in shape, measuring roughly 1.25 metres by 1.2 metres, it has a single shallow basin near its narrower end, and within that basin sits a small rectangular depression, about 11 centimetres by 12 centimetres, cut into the base.

That rectangular depression is the detail that complicates the picture. The working interpretation is that this stone may actually be an unfinished mill-wheel rather than a bullaun in the conventional sense, the rectangular recess being the kind of socket through which a central axle or spindle would pass. If so, it was abandoned mid-manufacture, for reasons that are now unrecoverable, and ended up in the same location as three stones of a quite different character. All four sit within what appears to be a possible ecclesiastical enclosure, the kind of roughly circular or oval boundary that often marks the perimeter of an early Irish monastic or church site. The grouping raises questions without fully answering them: whether the unfinished stone was always here, whether it was brought in from elsewhere, and what relationship, if any, it has to the religious function suggested by the enclosure.