84. Olioll Olum: son of Eoghan Mor; was the first of this line named in the Regal Roll to be king of both Munsters; for, before him, there were two septs that were alternately kings of Munster, until this Olioll married Sabina, daughter of the Monarch Conn of the Hundred Battles, and widow of Mac Niadh, chief of the other sept of Darin, descended from Ithe, and by whom she had one son named Lughaidh, commonly called "Luy Maccon;" who, when he came to man's age, demanded from Olioll, his stepfather, the benefit of the agreement formerly made between their ancestors; which Olioll not only refused to grant, but he also banished Maccon out of Ireland; who retired into Scotland, where, among his many friends and relations, he soon collected a strong party, returned with them to Ireland, and with the help and assistance of the rest of his sept who joined with them, he made war upon Olioll; to whose assistance his (Olioll's) brother-in-law, Art-Ean-Fhear, then Monarch of Ireland, came with a good army; between whom and Maccon was fought the great and memorable battle of Magh Mucromha (or Muckrove), near Athenry, where the Monarch Art, together with seven of Olioll's nine sons, by Sabina, lost their lives, and their army was totally defeated and routed. By this great victory Maccon not only recovered his right to the Kingdom of Munster, but the Monarchy also, wherein he maintained himself for thirty years; leaving the Kingdom of Munster to his stepfather Olioll Olum, undisturbed. After the battle, Olioll, having but two sons left alive, namely Cormac-Cas and Cian, and being very old, settled his kingdom upon Cormac, the elder son of the two, and his posterity; but soon after being informed that Owen Mór, his eldest son (who was slain in the battle of Magh Mucromha, above mentioned), had by a Druid's daughter issue, named Feach (Fiacha Maolleathan as he was called), born after his father's death, Olioll ordained that Cormac should be king during his life, and Feach to succeed him, and after him Cormac's son, and their posterity to continue so by turns; which (arrangement) was observed between them for many generations, sometimes dividing the kingdom between them, by the name of South, or North Munster, or Desmond, and Thomond. From these three sons of Olioll Olum are descended the Hiberian nobility and gentry of Munster and other parts of Ireland; viz., from Owen Mór are descended M`Carthy, O'Sullivan, O'Keeffe, and the rest of the ancient nobility of Desmond; from Cormac-Cas are descended O'Brien, MacMahon, O'Kennedy, and the rest of the nobility and gentry of Thomond; and from Cian [Kian] are descended O'Carroll (of Ely-O'Carroll), O'Meagher, O'Hara, O'Gara, etc. Olioll Olum had three sons named Eoghan, Cormac Cas and Cian [Kian]; and by his will he made a regulation that the kingdom of Munster should be ruled alternately by one of the posterity of Eoghan (or Eugene) Mór and Cormac Cas. This Cormac Cas was married to Oriund, daughter of King of Denmark, and by her had a son named Mogha Corb. From Cormac Cas, king of Munster, or according to others, his descendant Cas, who was king of Thomond in the fifth century, their posterity got the name Dal Cais, anglicised "Dalcassians ;" the various families of whom were located chiefly in that part of Thomond which forms the present county of Clare; and the ruling family of them were the O'Briens, Kings of Thomond. From Eoghan, the eldest of the sons of Olioll Olum, were descended the Eoghanachts or "Eugenians," who were, alternately with the Dalcassians, Kings of Munster, from the third to the eleventh century. The Eugenians possessed Desmond or South Munster. The head family of the Eugenians were the MacCarthys, princes of Desmond. From Cian, the third son of Olioll Olum, were descended the Clan Cian, who were located chiefly in Ormond; and the chief of which families were the O'Carrolls, princes of Ely. In the latter part of the third century, Lugaidh Meann, King of Munster, of the race of the Dalcassians, took from Connaught the territory afterwards called the county of Clare, and added it to Thomond. In the seventh century, Guaire, the 12th Christian King of Connaught, having collected a great army, marched into Thomond, for the purpose of recovering the territory of Clare, which had been taken from Connaught; and fought a great battle against the Munster forces commanded by Failbhe Flann and Dioma, Kings of Munster, but the Conacians were defeated. In the third century, Fiacha Maolleathan, King of Munster, and the grandson of Olioll Olum, had his residence at Rathnaoi, near Cashel, now called Knockraffan; and this Fiacha granted to Cairbre Musc, son of the king of Meath, and a famous bard, as a reward for his poems, an extensive territory, called from him, Muscrith Tire, comprising the present baronies of "Ormond," in the county of Tipperary. The Kings of Desmond of the Eoghan or Eugenian race, were also styled Kings of Cashel, as they chiefly resided there.

1 "Irish Pedigrees or the Origin and Stem of the Irish Nation", by John O'Hart is one of the best known Irish genealogical publications in the world. The first edition appeared in 1876, but was followed by several subsequent editions that added greatly to the overall size of the work. The most quoted edition was published in New York in 1923, twenty years after the author's death. It is worth mentioning here that the original work did not include and heraldic (coat of arms) information and that this was added to posthumous publications by unscrupulous publishers, presumably to increase sales. In general, O'Hart is a dubious source, at best, for such information (see quote below from Edward MacLysaght in regard to this topic).

John O'Hart was born in Crossmolina, Co. Mayo, in 1824. He received an excellent education with the intention of joining the priesthood. However, he instead spent two years in the constabulary (the police), after which he was employed by the Commissioners of National Education in Ireland from 1845, the first year of the Famine. He became an Associate in Arts at the Queen's University, and thereafter he was an active member of several scholarly societies. He was an avid genealogist and took a keen interest in Irish history, despite never receiving formal training as an historian. Politically he was an Irish nationalist, and in religious matters, a committed Catholic. Both of these factors permeated his work. He died in 1902 in Clontarf, Co. Dublin, at the age of 78.

O'Hart used many sources to compile the information that appears in his major work. His principal sources were Gaelic genealogies, like those of O'Clery, MacFirbis and O'Farrell. Along with the Gaelic annals, especially the Annals of the Four Masters, O'Hart was able to 'reconstruct' the medieval and ancient pedigrees that appear here. He also used later sources, like the works of Burke, Collins, Harris, Lodge and Ware to extend these lineages into the eighteenth and nineteenth centuries. But arguably the most important information contained in these genealogies came where O'Hart gathered the details directly from the families concerned, often from private papers or family tradition. These sections concern the later period, particularly post 1800, and are good for many specific localities like western Co. Clare.

There are two types of genealogies in O'Hart; the genealogies of the Gaelic families and the genealogies of Anglo-Norman and other later settlers. O'Hart made one important distinction in his treatment of these. Irish mythology records that every family was descended from a certain Milesius of Spain who in about 1700 BC led his followers to invade and conquer Ireland. The Christian monks who wrote these genealogies down in the 9th century, 2,500 years after Milesius, also added their own beliefs. So they recorded that Milesius was the 36th in descent from Adam! O'Hart, being both an ardent believer in the Gaelic myths and Christianity, followed their example. In his Gaelic genealogies a number representing the generation of descent from Adam precedes every generation. By contrast the Anglo-Normans and later invaders made no such claims, so O'Hart's genealogies of these families do not include these numbers. O'Hart showed, probably incorrectly, that every Gaelic family was descended from four of Milesius's family. These were his three sons, Heber, Ir and Heremon, and his uncle Ithe. These four were considered the 'stem' lines of the genealogies that followed.

While he undertook a great deal of research, using the majority of available published sources, many Gaelic scholars have superseded his work over the last 100 years. He was not familiar with the abundant unpublished Gaelic manuscript sources available. These have shown that many of his genealogies are incorrect for the years prior to 1600 AD. Furthermore, O'Hart was not a professional historian or genealogist, and had little training in using the esoteric sources he consulted. As a consequence he misunderstood a great deal about Gaelic society and culture, a world which had largely disappeared from Ireland long before he put pen to paper. He was also credulous in using the sources he did consult, believing that the myths were fact.

Despite these limitations, careful use of his work can be very productive. His genealogies for the years after 1600 have great value, and are often unavailable elsewhere. He was also able to consult many sources which have since been destroyed or lost. In the words of Edward MacLysaght, Ireland's most famous authority on the history of surnames, he 'made use of it almost daily'.

In relation to O'Hart and other similar publications, MacLysaght, however, also warns:

"The subject of Irish families is one in which much interest is evinced, but the popular books usually consulted and regarded as authoritative, particularly in America, are in fact unreliable. The inaccurate and misleading information thus imparted with cumulative effect is, however, much more deplorable in the armorial [coats of arms] sphere than in the genealogical. It is an indisputable fact that the publication presenting colour plates of Irish arms which is probably most widely consulted is no less than seventy per cent inaccurate, not only in mere detail, but often in points of primary importance and of an elementary kind. Apart from their many grotesque heraldic blunders the compilers of this work seem to have had a sort of rule of thumb; if they could not find arms for one Irish sept they looked for the name of another somewhat resembling it in sound: thus, for example, they coolly assigned the arms of Boylan to Boland. This frequently resulted in the arms of some purely English family being inserted in their book of "Irish Arms" the Saxon Huggins being equated with O'Higgins, and so on. When this arbitrary method failed them they fell back on the arms of some great Irish sept. To quote one instance of this: Gleeson, Noonan and McFadden are all given the arms of O'Brien, though none of these septs had any connexion whatever with the O'Briens or with each other. Consequently many Americans of Irish descent are in good faith using erroneous and often English arms derived from the spurious source in question.

A certain cachet has been given to this because, in the more recent editions of O'Hart's Irish Pedigrees, these same coloured plates have been inserted as if they were an integral part of O'Hart's book. The serious genealogist uses O'Hart with caution, if at all, for he is a far from reliable authority except for the quite modern period. John O'Hart, however, undoubtedly did a vast amount of research, no matter how he used the information he acquired: I know that some of these errors of ascription can actually be traced to him, but it is surely an injustice to him that his well-known name should be used as a cover for the propagation of false and often ludicrous heraldic statements."