It is easy to walk past such a thing without a second glance, yet it belongs to a category of object that has puzzled archaeologists and folklorists for generations.

The stone is a bullaun, a term used in Irish archaeology for boulders or flat stones bearing one or more cup-shaped depressions, typically formed by grinding or prolonged use. The hollow in this example measures roughly 47 centimetres across and 21 centimetres deep, which places it at the more substantial end of the scale. Bullauns are found across Ireland and are most commonly associated with early medieval ecclesiastical sites, though many stand at some remove from any obvious church ruin or holy well, as is the case here. Their original function remains debated: some were likely used as mortars for grinding grain or preparing medicines, while others acquired a ritual or votive significance over time, with the water that collects in their hollows traditionally credited with healing properties. The Ballythomas example sits in ordinary farmland, with no documented sacred site nearby, which gives it a quietly anomalous quality.