The mountain's importance may be inferred by the decision at the Synod of Raith Bressail in 1111 to make Nephin the northern boundary of the diocese of Cong. Gleann Neimhthinne is stated by John O'Donovan as being one of the seven constituent parts of Tirawley, the others being An Lagan, Breadach, Calraighe Maighe nEleag, Caoille Conaill, Ui Eathach Muaidhe and An Da Bhac.