To look at it now, the stone is unassuming, the kind that might easily be passed over. But local tradition holds that this was once an altar, a place where Catholic Mass was celebrated in secret during the Penal Era, when the practice of the faith carried serious legal consequences.

The Penal Laws, enacted in the late seventeenth and early eighteenth centuries, banned Catholic worship and stripped Catholics of property rights, political participation, and access to education. Priests who celebrated Mass risked imprisonment or worse, and congregations gathered wherever they could find cover, often on remote hillsides, in hollows, or behind field walls. Mass-rocks, as these outdoor altars came to be known, are found across Ireland, typically in elevated or sheltered spots that offered a view of approaching authorities. The Cloonta site fits that pattern. The hillock's flattish top, roughly thirteen and a half metres across, is partially enclosed by a bank of earth and small stones, running about nine metres on a north-northwest to south-southeast axis and standing half a metre high. The boulder that forms the focal point is built into this bank rather than set apart from it, suggesting the landscape itself was shaped, or at least used, with some deliberate purpose in mind.