The diocese of Kilmore was originally called Breifne (
Latin:
Tirbrunensis,
Tybruinensis or
Triburnia;
Irish:
Tír mBriúin, meaning "the land of the descendants of
Brian", one of the
Uí Briúin kings of Connacht). It was formally established as one of the dioceses approved by Cardinal
Giovanni Paparoni at the
synod of Kells in 1152. The 'Bishop of the Uí Briuin' used the style Bishop of Kells. The boundaries of the diocese were approximately the same as those of the ancient
Kingdom of Breifne as held under
Tigernán Ua Ruairc; which today would consist of almost all of
County Cavan, roughly the northern half of
County Leitrim, and parts of
County Fermanagh,
County Meath and
County Sligo. The boundaries were modified under the Norman colony with parts of Meath, including the town of Kells, being absorbed into the
diocese of Meath. In 1454, Bishop Aindrias Mac Brádaigh (Andrew McBrady) was given permission by
Pope Nicholas V to have the ancient church at
Kilmore, founded in the sixth century by
Saint Felim, to be the
cathedral church of the diocese. It was rebuilt and became known in
Irish as
An Chill Mhór (meaning
Great Church) and
anglicised as Kilmore, which gave its name to the diocese, a name which has remained ever since. Tir Brun / Kilmore was a territorial diocese, based on the kingdom of Breifne. From the late twelfth century the chieftainship of Breifne was contested between the Ui Raghallaigh or
O'Reilly sept in the east and the Ui Ruairc or
O'Rourke sept in the west. The bishops of the diocese came predominantly from the eastern end of the diocese, right down until the reformation. ==Kingdom of Ireland==