Killeavy - CiII Sleibhe in Irish means the Church of the Mountain. The Church referred to was originally founded by St. Moninna in the sixth century. She had founded her first convent at Faughart but after leaving this in charge of St. Orbilia she retired to the foot of Slieve Guillon.

        Remaining now are ruins of two churches, a western church and an eastern church. The western doorway, with immensely trimmed stones closely joined with a single slab forming the lintel, probably came from the ninth century. On the northern side of the cemetery there is a very large granite stone measuring seven feet long, five feet wide and about one and a half feet thick. This stone covers the supposed grave of St. Moninna - who died in the year 518 and here in days when the Pattern (which was the anniversary of the day on which a church had been dedicated to a saint) was celebrated, prayers were said at this spot and the pilgrim continued to her Holy Well further up the mountain, returning to this gravestone for the final prayer. The Pattern Day of St. Moninna was 6th July, but with the coming of persecution to the Catholic faith, these religious ceremonies were banned by law. The Pattern was revived in the year 1928 and seems to have survived until 6th July 1934. The scene was an historical setting for the Holy Year Pilgrimage on 4th August 1974. After the suppression of the Pattern in 1825, the existence of the holy Well was forgotten about ,but, was re-discovered by Father James Donnelly C.C. Meigh in 1880. The inscription on the Shrine at the Well now reads "Tobar Naoimh Blathnaidh - A.D. 498 - 1829".