A bullaun is a large stone, usually glacial or natural bedrock, into which one or more cup-shaped depressions have been ground, either by deliberate human effort or, in some cases, by the slow work of water and erosion. The deliberately made ones are most commonly associated with early Christian sites, where the hollows may have served as mortars for grinding, as receptacles for votive water, or as focal points for local ritual and prayer. The water that collects in them was, and in some places still is, considered to have curative properties.