Introduction to

the Genealogy

from the Collas to the MacMahons



The following pages represent the lineage of the MacMahons of Oriel as constructed by mediaeval genealogists and as reconstructed and modified slightly by scholar Don Schlegel, a man who has studied these charts in depth as he searched and sifted for his own roots, the MacDonalds of Scotland, who were descended too from the Collas.


Don and I will attempt in this page to explain and illustrate to you what we know about the lineage.  We will update this page as more information is unearthed.  Please note that the links embedded in the page are intended to allow you to view a specific chart related to that segment of text.  After viewing the chart, you may return to this page to continue the story.  Alternatively, you may read the story and then simply flip the charts, page by page.  There are nine in all.


After conquering the Ulaid, the Collas and their people settled the area that then became known as Airghialla, after the tribal name of the entire group, consisting of the Collas, their followers, and their descendants.  The first page in the charts (na tri Colla) shows the three brothers and the tribes and family names descended from them.  The tribes and Clans further settled and occupied different portions of Oriel as illustrated on the map on the page: Oriel ~ From the Collas to the MacMahons.


The MacMahons descended through the line of the Ui Chrimthainn, a particular tribe descended from Chrimthann Liath, the great great grandson of Muredach Colla da Crich, the first King of Airghialla. (Ui Chrimthainn)  You can see on this chart that Eochaid, son of Crimthainn Liath was King of Airghialla and a contemporary of Saint Patrick.  Saint Patrick was based in the modern day town of Downpatrick and the literature places him sometimes in Armagh, the former on the periphery and the latter in the heart of Oriel.  Within the Ui Chrimthainn were various clans. 


The MacMahons and the O’Carrolls were of the Clan Nadsluaig (Clan Nadsluaig).  This chart shows Clan Nadsluaig descending from Fergus, son of Nadsluag, grandson of Eochaid.  As you follow this chart, you can see that the Lords of Fernmaig were of this line, including Mathgamna, from whom came the name MacMahon.  From the line of Mathgamna come both the families of O’Carroll, known as the Kings of Oriel at the height of its power just prior to the coming of the Normans, and the MacMahons, the latter descending from Niall, brother of Murrough O’Carroll the last O’Carroll King of Oriel.


Looking at chart 4, we see Eochaid, first MacMahon King of Oriel, rising to power in 1250 AD and dying in 1273. (MacMahon) The surviving MacMahon lines then spring from Roalbh, Lord of Dartree, then his son Aodh, then through Brian Mor, then his son Ardgal.  The remaining charts all show the surviving branches of the MacMahons spring from Ardgal, died 1427.  Clan Ardgail MacMahon


Chart 5 shows the Clan Ruaidri meic Ardgail MacMahon and their relationship to MacMahon of Lucht-Tighe (the Monaghan MacMahons), MacMahon of Farney, and MacMahon of Dartree


These charts show the family lineage into the late 1600s and mid 1700s in some cases.


A new discovery: Our dna project has identified a branch of MacMahons previously only rumored to exist and known by few.  That is the branch of MacMahon descended from Maguire and not from Niall Mac Mathghamhna.  You may see that lineage here:


Clann Mahon Maguire


Terry Mathews of Aisling, Boyher, Rockcorry, County Monaghan is a participant in the dna project who matches Maguire and who also represents the Maguire MacMahons.  For more detail on our dna project, see this page: McMahon DNA Project




Author’s Note: Many thanks to Donald Schlegel for assembling this very complex genealogy.  There are numerous hours of detailed research and then tedious effort in assembling this information.




Enter here to follow the lineage from the three Collas to the MacMahons:

Next Page: na tri Colla

John McLaughlin assembled a listing of the MacMahon pedigree from all of the various sources:

A Listing of All Genealogy Sources for MacMahon

Return to: The Rise of the MacMahons

Next Chapter: Faerie Forts

Return to Index

updated 1-13-06