A bullaun is a large stone, usually a boulder, with one or more cup-shaped depressions ground or pecked into its surface. The hollows collect rainwater, and across centuries of folk tradition that water has been credited with curative properties, particularly for skin complaints and eye ailments. The stones turn up in early ecclesiastical sites, in field corners, beside ruined churches, and occasionally in the open countryside, and their origins are genuinely uncertain, spanning a period from the early medieval into later centuries.