Tradition holds that Fenagh Abbey was founded in the sixth century by St Caillín, becoming one of the most important centres of early Christianity in Connacht. Situated in the heart of ancient Breifne, the monastery developed a reputation as a place of learning, attracting scholars and students who came to study scripture, theology, and the traditions of the Irish Church. Its influence extended well beyond the surrounding countryside, and Fenagh became closely associated with the preservation of Ireland's religious and cultural inheritance.

The monastery was also a place where history and memory were carefully preserved. Its most celebrated legacy is the Book of Fenagh, a remarkable collection of religious writings, genealogies, poems, and accounts of the life of St Caillín, compiled in the fifteenth and sixteenth centuries from much older traditions. The manuscript offers a glimpse into a world in which faith, learning, and the stories of a people were inseparable.

Although the original monastery has long since disappeared, the medieval church ruins and ancient ecclesiastical remains still mark the landscape. Fenagh stands as a reminder of the extraordinary contribution made by Ireland's early monastic communities—not only to Christianity, but also to the preservation of knowledge and tradition through centuries of change.