These altars, which escaped the attention of early Ordnance Survey mapmakers in 1834, were finally documented during the 1848 revision. According to J. Byrne, whose account was preserved in the OS Revision Name Book, these were “six old Roman Catholic altars for the celebration of mass”, serving as crucial gathering points for communities forbidden from practising their faith openly.

During the Penal Laws period, which stretched from the late 17th century through to Catholic Emancipation in 1829, Irish Catholics faced severe restrictions on religious worship. Priests risked imprisonment or death for saying mass, whilst congregations gathered in secret at remote outdoor locations known as mass rocks or penal altars. The six altars near Muff represent one such network of worship sites, strategically positioned to serve different communities whilst avoiding detection by authorities.

What makes these particular altars intriguing is their late recognition by official surveys; they operated in plain sight yet remained unmapped for decades after Catholic Emancipation. Today, they stand as powerful monuments to religious resilience, marking places where communities risked everything to maintain their spiritual traditions. Their survival offers visitors a tangible connection to a time when faith itself was an act of defiance in rural Donegal.