An Analysis of the McMahon Pedigree

Book of Leinster 1170 A.D.

p. 338 Col. C (O Cearbhaill)

Gt. Ua Cearbhaill

Donchadh m Con caisil m. Donaill m Matgamna m Laedcen

m Cearbhaill m Mael Poil m Fogartach m Ruadrach

m. Mail fogartaigh m Airach m Aithecda m Mael duib

m Cronan m Fergusa m Nad sluaig, etc



Mael Poil





Con caisil

Donnchadh O Carroll (d. 1168)

Analysis: This is a historical pedigree of the O Cearbhaills, verified by annal entries.

Book of Ballymote

Pilip m. Briain m. Aeda m. Roailbh m. Eachada m. Mathgamna

m. Neill m. Donnchada m. Concaisil m. Domnaill m. Mathgamna

onabar Meg Mathgamna m. Fogartaich m. Ruadrach m. Mailifothardaig

m. Artraid m. Echach m. Maelduibh m. Mailfogartaich m. Ronan

m. Fergusa m. Nadsluaigh.




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Mathgamna (a quo) Mael Poil

Domnaill Cearbhaill

Con caisil Laedcen

Donnchadha Matgamna

Neill ['the proud'] Donaill

Con caisil

Donnchadh O Carroll (d. 1168)

Analysis: It is evident that this pedigree for McMahon was derived from the earlier Book of Leinster pedigree for O Cearbhaill. An entire string of names (Donnchadh-Con caisil-Domnaill) repeats in both the pedigree for McMahon and that of O Cearbhaill. The pedigree makes the McMahons a branch of the same stock of the O Cearbhaills, which is probably correct. It is obviously non-historic though for two reasons.

1. Neill 'the proud' who may have lived as late as 1239 appears two generations before Donnchadh O Cearbhaill,

who died in 1168.

2. The string of repeating names. This is evidence that this is a manufactured pedigree by an Irish scribe.

Book of Lecan




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Matgamhna Mael Poil

Donaill Cearbhaill

Con Caisil Laedcen

Donnchadh Matgamna

Neill Con caisil

Mathgamhna Donnchadh O Carroll, d. 1168


Neill 'the proud'


Analysis: This pedigree is at least plausible at first glance. Here we have a Neill 'the proud' two generations after Donnchadh O Carroll, which is about where he should appear based on the annal entries. But we also encounter the same problem that appears in the Ballymote pedigree of a string of names (Donnchadh-Con caisil-Donaill) that appears to have been lifted directly from the O Carroll pedigree from the Book of Leinster.

Based on this, we can probably state the Ballymote and Lecan pedigrees were derived from the same or similar source. The Lecan version though has two Neills. Through the first Neill Ballymote and Lecan are identical. In Ballymote it is obviously this first Neill who was considered Neill 'the proud.' There is no other candidate in the pedigree.

After the first Neill, Ballymote and Lecan differ in that Lecan has some extra names not found in Ballymote. Both end in

Pilip s. Brian so a comparison is straightforward.

Ballymote Lecan

Ruadrach Ruadrach

Fogartach Fogartach

Mathgamna (a quo) Matgamhna (a quo)

Domnaill Donaill

Concaisil Con caisil

Donnchadha Donchadh

Neill Neill

Matgamna Matghgamhna

Eochadha Magnusa

Roailbh Neill

Aeda Eochaidh

Briain Roailbh

Pilip Aedh



What is going on in the Lecan pedigree is that some scribe probably realised that the Ballymote pedigree was impossible, for the reasons stated above; and what we find in Lecan was an attempt to re-position Neill 'the proud' in a generation that would better fit the annal entries for him. So the names Neill-Matgamhna were doubled in Lecan and the name Magnus was added as well to flesh out the generations.

These two pedigrees then are just variations or re-writings of each other. Neither is historical. Both contain the "stolen" string of names from the earlier authentic O Cearbhaill pedigree.

National Library G2



Mael Poil





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Faelan Donaill

Aedha Con caisil

Neill Donchadh O Carroll, d. 1168




Analysis: The only real problem with this pedigree is that it places Neill 'the proud' in the same generation as Donnchadh O Carroll, which would appear to be incorrect, but not necessarily so.

It does not have the glaring forgery of the string of names in Ballymote and Lecan. For that reason alone it should be

taken seriously as a possibility.

A second reason this pedigree should be given some weight is the fact that it agrees with the information in the Lecan

fragment, kindly translated by Katherine Simms.

"Aodh son of Fáolán had another son, that is, Niall the Arrogant (Uaibrech). It was through the oppression (tre truma) of his lordship (a tigernais) that chieftains of the Mughdhorna of Oirghiall (barony of Cremourne, co. Monaghan) fled (do techsead) into Trian Conghail, so that from their descendants (ono geineamain) is named (sloindter) the land they inhabit (aitrebait) today (aniu), that is, Mourne (Co. Down)

Lec. (facs.), fo. 79r., col. d, line 35."

The Lecan fragment co-exists with the full pedigree of the McMahons in that manuscript. It was obviously taken from a source which did not agree with the Lecan/Ballymote McMahon material which is clearly manufactured. As such it is probably closer to the true descent of the McMahons than any other pedigree source.

The Lecan fragment is also found in a much later 17th century manuscript, Trinity H4.31, quoted by Shirley in his "Farney."

There are several later McMahon pedigrees of some interest. The Leabhar Donn (ca. 1500) contains a pedigree which is identical to Lecan except that the string of names in that manuscript (Donnchadh-Concaisel-Domnaill) are connected properly to the Cearbhaill in the O Carroll pedigree. This is simply another later re-working of the Lecan/Ballymote pedigree of no particular importance.

Leabhar Donn Lecan

Ruadrach Ruadrach

Fogartaigh Fogartach

Mailpoil Matgamhna (a quo)

Cerbaill Donaill

Laidgnen Con caisil

Mathgamna Donchadh

Domnaill Neill

Concaisil Matghamhna

Dondchadha Magnusa

Neill Neill

Matgamna Eochaidh

Magnusa Roailbh

Neill Aedh

Mathgamna Brian





A very late pedigree for the McMahons is quoted by Shirley in his "Farney," apparently based partly on the Lecan fragment discussed above and referred to by O'Donovan (Topographical Poems) as the true descent of the McMahons.

Shirley’s “Farney” (based on Trinity H4.31)

20. Ruadragh

21. Fogarty

22. Maelpoil

23. Carroll, Lord of Farney

24. Laidgnew, killed AD 987

25. Mahon, killed at Clones, AD 1022

26. Donell

27. Cucashell O'Carroll, Lord of Farney, died AD 1123

28. Donogh

29. Niall (1196-1217)

30. Mahon

31. Magnus

32. Hugh

33. Mathghamhain or Mahon

34. Eochaidh Mac Mahon, killed AD 1273. Lord of Oriel.

35. Roolb, or Rory Mac Mahon, killed AD 1323.

36. Aodh d. 1344

37. Brian Mor became king, 1365; sl. 1372

This pedigree is identical to that of the Leabhar Donn, in that it contains the name Cearbhaill and the Niall-Mahon-Magnus string of names originally from Lecan. It differs slightly though in that Trinity H4.31 contains a later version of the Lecan fragment 'Niall the Arrogant (Uaibhreach) is another son of that Aodh, and it was with the oppression (le truime) of his taxation (a chiosa) and his lordship (a thiagernus) that the chieftains of Mugarna Oirghiall fled (ro theichseatt) into Trian Conghail, and it was from that migration (don tsiubhal sin) that the land that many of them (moran diobh) inhabit (attreabhaid) today (aniugh) is called (sloinnter), that is, Mugharna of Iveagh (Mourne, Co. Down).

This pedigree differs from the Leabhar Donn in making an Aedh or Hugh the son of Magnus s. Mahon s. Neill. This Aedh is clearly intended to be the Aedh s. Faelan of the original Lecan fragment (but here edited to remove the name Faelan). This would make Neill 'the proud' a son of this Aodh, his brother being Mathghamhain (No. 33) in the pedigree.

Because this pedigree is simply a combination of the discredited Lecan/Ballymote and Leabhar Donn variants, no particular significance can be attached to it. The evidence of editing out the name "Faelan" in the original source is particularly damning.


In summary, the only pedigree of the McMahons not completely defective is the National Library G2 variant. Like Ballymote and Lecan it is a very early source; perhaps even earlier than either of these early 15th century manuscripts, although the pedigree appears to be a gloss added by a hand other than that of the original scribe at an unknown date.

The only questionable point in the G2 pedigree is whether Neill 'the proud' and Donnchadh O Carroll could have been in the same generation (both great-grandsons of Matgamhna). The annals would appear to place these two men in different generations, Neill being a generation or two younger than Donnchadh O Carroll Donnchadh O Carroll makes his first appearance in the annals (Four Masters) in 1133 and is thereafter mentioned continuously until his death in 1168 – an untimely death - mangled with his own battle-axe by one of his own chieftains.

If we assume he was at least 20 in 1133 when his career began than he would have been 55 years old in 1168, but probably much older.

The annal entries for the McMahons are much less substantial. In 1181 an unnamed McMahon appears, followed by Neill McMahon in 1196.

Then follows a reference to another unnamed McMahon (but probably Neill) in 1206. In 1207 Neill is again identified (McCarthy fragments) but called the "son of McMahon" in the annals of Loch Ce.

Unfortunately it is not clear whether the Annals of Loch Ce and the McCarthy fragments are describing the same incident in this year.

In 1211 we have another reference to an unidentified McMahon (called the "son of McMahon" in Loch Ce); then in 1217 another reference to the "son of McMahon."

Neill is thus last identified by name in 1207 and it is possible the later references are to his son. In 1239 we have another unidentified McMahon in the annals; but all later references are clearly identified.

So the last entry in the annals which could possibly refer to Neill was in 1239. But the sudden references to a "son of McMahon" from 1207 on would seem to indicate that Neill had died and his son was now "the McMahon."

The annals thus do not establish an accurate date for the lifetime of Neill 'the proud' McMahon. He probably came into some prominence for the first time in the annal entry of 1181; but we do not know for sure whether he died sometime around or shortly after 1207 or continued to head the family until 1239. The only thing we know for sure is that he did not rise to power until after the last O Carroll is mentioned in the annals in 1183.

The dates for Donnchadh O Carroll 1133-1168 (pre-mature death) and Neill McMahon (1181-1207 or later) do not seem to place them in the same generation as stated in the G2 pedigree. But perhaps Neill was a youngest son born some twenty years or more after his oldest siblings as is so often the case in large families. That might go a long way towards explaining the apparent discrepancy in their ages as reflected in the annals.

Analysis by:

John McLaughlin

summer 2003


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