 The traditional territory of the Uí Briúin Bréifne was known as the kingdom of Bréifne, which included the modern Irish counties of Leitrim and Cavan, along with parts of County Sligo.It is speculated that Breffny derives its name from a pre-Celtic substrate language spoken in Ireland meaning 'ring' or 'loop', therefore making Breifne one of the oldest placenames in Ireland, dating prior to 500 B.C.The two principal families of Uí Briúin Bréifne were the O'Rourkes and O'Reillys, who after a great battle in 1256, split the kingdom into East Bréifne and West Bréifne.