Mass-rocks are exactly what the name suggests: flat stones or natural outcrops that served as improvised altars, used by priests and their congregations when church buildings were either seized, demolished, or forbidden. They are scattered across Ireland in considerable numbers, often on hillsides, in hollows, or at the edges of fields, chosen for their remoteness from roads and from the eyes of authorities.

The Penal Laws, which reached their most restrictive form in the late seventeenth and early eighteenth centuries, prohibited Catholic clergy from openly ministering and placed severe constraints on Catholic worship more broadly. Gatherings at mass-rocks were therefore clandestine affairs, with lookouts posted and the community bound together by shared risk. The rocks themselves were rarely elaborate; their significance was entirely in their use rather than their form. Many have since become quiet local landmarks, known to the surrounding community even as the circumstances that created them have passed out of living memory. The Glebe example belongs to this wider pattern of informal sacred sites that persisted through a long period of religious suppression.