Clanmahon takes its name from the Irish Clann Mathúna, originally Cloinne Mathghamhna, "Mathgamhain's tribe," the ruling Gaelic Irish dynasty in the area in the Middle Ages. The personal name Mathgamhain means "bear" and was a common name among warriors.[1]
Map of Breifne in AD 700; Clanmahon is seen near to the "Cairpre Gabra" tribe.
The descendants of Tomas Mór O'Reilly, king of East Breifne 1384–92, were rulers of Clanmahon in the 15th century; Tomás was the son of Mathgamain Ua Raighillaigh. The Uí Shioradáin (O'Sheridans) were a vassal tribe.[5] The Ua Raghallaigh (O'Reillys) were also powerful landowners until the 16th century.[6] According to the Annals of the Four Masters, in 1537, "The son of O'Reilly (Brian, the son of Farrell), a great loss in his own country, was slain by the people of the English Lord Justice[Leonard Grey, 1st Viscount Grane], who came to commit ravages in Clann-Mahon."[7]
