Mass-rocks are among the quieter survivals of the Penal era in Ireland, the period running roughly from the late seventeenth century through much of the eighteenth, when Catholic worship was suppressed under a series of legislative restrictions. With church buildings banned or inaccessible, congregations gathered outdoors, often in remote or sheltered spots, and a large flat rock would serve as the priest's altar. The practice left behind a scattered geography of improvised sacred sites, most of them unmarked on any official map, known mainly through local memory.

The Penal Laws, introduced following the Williamite victory and consolidated in the early 1700s, prohibited Catholics from building churches, attending Mass openly, or educating their children in the faith. Priests were required to register with authorities or face transportation; those who did not were liable to prosecution. In practice, enforcement was uneven and varied by region and by decade, but the threat was real enough that rural communities developed habits of secrecy, posting lookouts, meeting at dawn, and choosing sites with natural cover or good sightlines across open ground. A mass-rock was not merely a convenience; it was a practical response to the possibility of interruption. The Cosmona site fits into this wider pattern, one of many such locations recorded across Connacht, where the landscape of bogs, drumlins, and quiet townlands offered the kind of obscurity that congregations needed.