Placenames of Bréifne
In the 10th and 11th centuries the O'Ruairc kings of Breifne vied for the title of king of Connacht, four different O'Ruaircs cited with that honor. During the 12th century the reign of Tiernan mor O'Ruairc, the kingdom of Breifne (Brefny, Brenny, etc) was said to comprise most of the modern counties of Leitrim and Cavan, and parts of Longford, Meath, Fermanagh, and Sligo in north-central Ireland. The modern Diocesan map (at right) indicates an approximate extent of Breifne and Conmaicne back in the the 12th century, when the boundaries of many Irish dioceses were set.