The Rise of the MacMahons


Kings of Oriel



'During the closing centuries of Gaelic rule in Ireland, Monaghan was frequently described in English state documents as 'Mac Mahon's Countrie'' ~ Peadar Livingstone

The Mac Mahons rose to power during tough times.  The English invasion of Ireland had begun but the Irish were slow to see it in the national context, preoccupied as they were with their individual tuathas or kingdoms.  The MacMahons replaced the O'Carrolls as the lords of Oriel after the latter were killed by the Normans and the remainder of the O'Carroll family apparently migrated out of Oriel.  King Henry had granted lands in Oriel to his own Norman Lords but these men had no ability to take control of those lands as long as the O'Carrolls remained as Kings.  ( for more information see The Ua Cerbail Kingdom of Airgialla )  As late at 1189, the year of his death, Murchadh O'Carroll was in control of much of Airghialla, though the literature reads as though he had his hands full trying to keep the Kingdom together against the actions of the Normans.  He was succeeded by Muircheartach O'Carroll.  In 1194, Muricheartach was captured by the Normans and subsequently blinded and then hanged.  With that act, the O'Carroll reign as Kings came to an end and other families vied for the position, with the princes of Fearnmhaigh, the 'Alder Plain' in what is now western Monaghan County, succeeding the O'Carrolls.  According to Livingstone, the invasion of the Normans left only three clans with any power at all.  These were the Ui Baigeallain (O'Boylon) in Dartraige, the Mac Murchadha family in Truagh, and the MacMahons.  The literature also suggests that the O'Hanlon family had considerable power and vied for control of Oriel, holding the title of King on a couple of occasions between the time of the O'Carrolls and the time when Eochaid established himself firmly as the first Mac Mahon King in 1250.

The MacMahons arose from the Ui Nadsluaig family of the Airghialla tribes.  Their ancestor was Mathghamhain, the 'bear-like' person, son of Laidcnen, King of Fearnmaig:

Annals of the Four Masters:
M1022.13 - Mathghamhain, mac Laidhgnéin, mic Cerbhaill, tigherna
Fernmhaighe, do mharbhadh h-i c-Cluain Eoais lá Cathal ua Críocháin.

Annals of Tigernach:
T1022.9 - Mathgamain mac Laidhgnen, maic Cerbaill, rí Fernmuighe, do
marbadh do Cathal o Crichan a Cluain Eoís.

Irish Texts online

Mathghamhain was slain in 1022 by Cathalan ua Crichain, his cousin and the next reigning King of Fearnmaig.  (Mathgahmna is a recurring name throughout early Irish history and is not restricted to this tribe or clan).  The Mac Mahon reign began in about 1250 with the rise of Eochaid Mac Mahon of Lough Leck to the position of King of Oriel and lasted until Oriel came to an end with the beheading of the last Mac Mahon King during the Rising of 1641. 

But it was Niall Mac Mathghamhna that gave rise to the Mac Mahon kingship, a generation or two before Eochaid.  The very first reference to the Mac Mahon name in the Annals comes in 1181, with this:

1181 AU (Annals of Ulster)

Aedh Mac Murchadha, royal chief of Muinnter-Birn and the Airthir and the Cantred, was killed by Mac Mathgamna in treachery, at a meeting.  (Some light can be shed upon the context in which this takes place by reading the document: Ulster Place-names Journal Ainm, vol. 7: Arthur, J. B., "Mourne", 1952-3: appended)

The references do not make clear whether this action was taken by Niall MacMathgamhna or his father.  But over the course of the next fifty years, the MacMahons were critical in establishing themselves as a force in Oriel and in holding the Normans at bay.  (see From Bandits to Kings)  Clearly it was these actions that led to Eochaid's ability to rise to the position of the first formally recognized Mac Mahon King of Oriel in 1250.

At some point the Lords of Fearnmaigh relocated from western Monaghan, the original 'Farney' located in the area around Clones and established themselves in modern day Farney, the current barony around Carrickmacross.  There is no definitive date for this but it appears to have taken place around the time of Niall Mac Mathghamhna, circa 1196.  The reasons for the move are also unclear but no doubt pertained to the various pressures caused by either the Normans or the Maguires in neighboring Fermanagh.  The genealogy of the MacMahons, though obviously constructed after their rise to power and containing errors, appears to have them legitimately descend from the Fearnmaigi.  The Mac Mathghamha surname is said to have arisen at Lough Leck in southwestern Monaghan, suggesting that the move took place either before or during the reign of Niall and before Eochaid's rise to power.  Still, the Mac Mahons were to recall their roots in Fearnmaigh, and Clones remained an important place for the MacMahons.

The Mac Mahon reign was characterized by continuous turmoil due to constant threats by the Normans in Louth, the O'Neills of Tyrone, the Maguires in Fermanagh, and the O'Reillys of Cavan.

The family had humble origins at Lough Leck but were able to establish themselves in Monaghan town.  At the start of Eochaid's reign Oriel was much diminished from its former size under the Collas or subsequent rulers.  The Mac Mahons held reign in the western portion of modern County Monaghan and had a tentative hold on Monaghan town.  But the Mac Mahons were to consolidate their powers, take advantage of circumstances and through aggressive action were successful in increasing the size of their territory over the coming years. 

The family seemed to hold the philosophy that the best defense was offense.  By 1300 the MacMahons gained control over much of the area of modern day County Monaghan.  Eoachaid was strong enough in 1264 to resist Aodh O'Neill's claim as King of Airghialla. 

When Eochaid was slain by O'Hanlon and the Kinel-Owen in 1273, Livingstone suggests that Eochaid's son Roalbh succeeded him but it is not clear how long Roalbh lasted.  In 1284 a Brian MacMahon (another son of Eochaid) is mentioned as chieftain.  Brian died in 1311 and his brother succeeded him but was killed in 1314. (There may be some confusion here: Brian and Roalbh were both sons of Eochaid and it could be that Brian succeeded Eochaid and was then succeeded by Roalbh - see MacMahon

Murchadh Mor Mac Mahon succeeded as the next chief of Oriel.  (Oriel is an anglicized version of the word Airghialla)  Murchadh Mor seemed to focus on conflicts in the western portion of the territory and neglected the east.

The MacMahon reign was characterized not only by fighting with neighboring lords but also by fighting among the Mac Mahons themselves.  In 1331 Sean MacMahon of Farney was able, with the help of the Normans, to attack and slay Murchadh Mor Mac Mahon.  Sean seized the chieftaincy of Oriel and held it for ten years.  Sean was expelled in 1342 by Hugh Mac Mahon, who named himself as chief.  Sean apparently returned the next year to lay claim once again but was killed in the conflict.  Hugh died that same year and his successor was Murchadh Og Mac Mahon.  Murchadh died after just one week and was succeeded by Manus Mac Mahon, grandson of Roalbh.

The constant fighting and change in Kings held true in subsequent years.  Livingstone provides great deal on this era, if you care to learn more.  Other sources include the Annals of the Kingdom of Ireland by the Four Masters, the Annals of Ulster and Miscellaneous Irish Annals, edited by Séamus Ó hInnse and published in 1947 by the Dublin Institute for Advanced Studies.  Excerpts from a document called the 'Black Rent' provide interesting insights into the reign of the MacMahons.

To gain insight into the Mac Mahon Overlordship of Airghialla, the pressures they endured, and the changes that took place, then follow this link to a detailed compilation of all the references in all of the pertinent Irish historical texts to the MacMahon kingship of Oriel, known as the MacMahon Irish Annals.  This is an excellent resource for viewing the recorded history of the MacMahon Kingship of Oriel from its beginning until the references end at 1608.  As you read the Annal entries you can actually follow the changes in leadership by looking at our Mac Mahon Genealogy charts.

Livingstone's work focused primarily on the conflicts within Monaghan and provides little or no information on the conflicts on the larger scale.  It is clear, though, that the conflicts that occupied the Mac Mahon reign, including the conflicts between different branches of the family, were nothing new.  Reading the Annals of Ulster one can see that there was constant raiding between neighboring clans and families that was simply common practice dating back for hundreds of years.  This was a way of life.  Perhaps it can be viewed as a fight for survival, survival of the fittest or most aggressive.

Much has been made of the difficulty the Mac Mahons had with the O'Neills.  In The Annals of the Four Masters, there is recorded a victory by Hugh O'Neill over the people of Oriel and Fernmaighe in 1358.  And then in 1368 the following is recorded:

    'A great army was led by Niall O'Neill, king of the Kinel-Owen, who was joined by the chieftains of the entire province (of Ulster), into Oriel, to attack Brian Mac Mahon; and they pitched a camp in the very centre of the territory.  Mac Mahon offered him great terms, namely, to cede one half of the territory of Oriel to Niall, the son of Murrough MacMahon, son of Brian na g-Coileach n-Oifrinn, ie: he who had been lord over the territory before himself; and other great gifts to O'Neill himself, as (restitution) for (the death of) MacDonnell.  O'Neill consented to make peace with him on these conditions; but the son of Murrough Mac Mahon and Alexander Oge MacDonnell, lord of the Gallowglasses, without Neill's permission, marched, with one accord, with three battalions of kerns against MacMahon, and made assault upon his fortress; but MacMahon and his household, being upon their guard, armed and accoutered within their fortress, responded without delay to the attack; and a fierce and furious conflict ensued, in which they (the assailants) were defeated by Mac Mahon.  The son of Murrough Mac Mahon, Tanist of Oriel (ie: designated successor as king); Alexander, the son of Turlough MacDonnell....were slain.'

And then in 1370:

    'Niall O'Niall, Lord of the Kinel-Owen, routed Brian MacMahon, Lord of Oriel; and a very great number of Mac Mahon's people were cut off by slaying and drowning....'


The passages above are typical reading from the Annals and if anything provide greater detail than most entries.  As you can see, these fellows didn't rest much between fights with their neighbors.

Another common and fashionable practice during the 14th century by the Mac Mahons and other Gaelic chieftains was to raid the territory known as the Pale (see map above) to steal cattle.  From this practice (no doubt from the perspective of residents of the Pale) emerged the saying 'Beyond the Pale'.  The Pale sounds as though it were a sort of unsafe haven for settlers brought in by the Norman rulers of England.  It seems that the MacMahons were able to extract a payment from residents of the Pale in return for ceasing these raids.  Yet the very existence of the Pale and its English occupants was a constant threat to the progress of the MacMahons in extending their range of influence in that direction.  The Pale did provide a place of refuge for those families displaced by the MacMahon aggressiveness.

To be fair to the Mac Mahon Clan, we have been told by numerous sources not to judge the family too harshly.  The constant fighting and raiding was a standard practice at the time and was seen as virtuous.  While in Ireland recently, I was told by a woman that we Mac Mahons are all 'rogues'.  She then told me that she didn't mean that in a bad way. In fact, the ability of the Mac Mahons to retain control of Oriel for so long is seen by many as a tribute to their valour and prowess.  And the reason that the Mac Mahons are remembered today in County Monaghan is because their reign endured for some 400 years, no small feat.


In 1372, John O'Dubhagain wrote:

O'Cearbhaill, O'Duibhdara
Chief kings without fratricide,
Men who have attended on each poet,
Are over the Oirghialla without reproach.

Chief kings in place of these,
Are the MacMathghamnas and Maguidhir,
Well with you their clemency, their rule,
noblest races of the Oirghialla

   ~ from The topographical poems of
John O'Dubhagain and Giolla na Naomh O'Huidhrin.

Edited in the original Irish,
from mss. in the Library of the Royal Irish Academy, Dublin;
 by John O'Donovan. Dublin, Printed for the
Irish Archaelogical and Celtic Society, 1862, p. 28-29


One outcome of the continual fighting and expansionist practices was the gradual emergence of three centers of power of Mac Mahon chieftains within Oriel.  One was in Monaghan town itself, another was Lisnagore, near Newbliss in Dartrey and the third was in Lurgans in Farney.  Each area came to be governed by a local Mac Mahon chieftain and the importance of the title King of Oriel diminished in terms of the practical power or influence in each of these three distinct parts of the Kingdom.  The story continues in the next chapter on the three baronies of Oriel...

Next Chapter: The Three Baronies

Ireland History in Maps (1200 AD)

Ireland History in Maps (1300 AD)

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