|Conor Myles John O'Brien, 18th Baron Inchiquin|
|Historic seat||Dromoland Castle|
The Dalcassians (Irish: Dál gCais [d̪ˠaːlˠ gaʃ]) were a Gaelic Irish tribe, generally accepted by contemporary scholarship as being a branch of the Déisi Muman, that became a powerful group in Ireland during the 10th century. Their genealogies claimed descent from Cormac Cas, who is said to have lived in the 3rd century AD. Their known ancestors are the subject of The Expulsion of the Déisi tale and one branch of their blood-line went on to rule the petty kingdom of Dyfed in Wales during the 4th century; probably in alliance with the Roman Emperor Magnus Maximus.
Brian Bóruma is perhaps the best-known king from the dynasty and was responsible to a significant degree for carving out their fortunes. The family had built a power base on the banks of the River Shannon and Brian's brother Mahon became their first King of Munster, taking the throne from the rival Eóganachta. This influence was greatly extended under Brian who became High King of Ireland, following a series of conflicts with Norse and other Irish tribes, before dying famously at the Battle of Clontarf in 1014. Following this the Dál gCais provided three more High Kings of Ireland; Donnchad mac Briain, Toirdelbach Ua Briain and Muirchertach Ua Briain.
From the 12th–16th centuries, the Dál gCais contented themselves with being reduced to the Kingdom of Thomond. They attempted to claim the Kingdom of Desmond for a time, but ultimately the MacCarthys held it. The Kennedys also held the Kingdom of Ormond for a time. Some of the better known septs included O'Brien, Moloney, MacNamara, O'Grady, O'Gorman, Kennedy, MacMahon, McInerney, and Clancy. During the 13th century Richard Strongbow's relatives the Norman de Clares attempted to take Thomond, but the Dál gCais held firm.
It wasn't until the 16th century, unable to be defeated militarily, they agreed to surrender and regrant their kingdom to Henry VIII Tudor, joining the nobility of the Kingdom of Ireland. Their realm was renamed County Clare, though they remained influential. In later times, remarkable figures include writer Standish James O'Grady, who is called "Father of the Celtic Revival" and William Smith O'Brien who played a leading part in the Young Irelander Rebellion of 1848. In diaspora, prominent figures have included Marshal Patrice de Mac-Mahon, President of France, as well as John F. Kennedy and Ronald Reagan, who were both Presidents of the United States.
Origins, Déisi Muman vs. Deirgtine
In their own genealogies, the Dál gCais traced their line back to their eponymous ancestor and progenitor Cormac Cas, who is said to have lived in the 2nd to 3rd century. They make him a second son of Ailill Aulom from the Deirgtine, a King of Munster and Leath Moga more generally, associated in a story with the goddess Áine of the Tuatha Dé Danann during the Cycles of the Kings of Irish mythology. Cormac Cas himself was purported to be the younger brother of Eógan, founder of the Eóganachta, who would go on to rule Munster for many centuries. While this was taken on face value for a long time, later Irish scholars came to question its validity, regarding it as a politically motivated fabrication. The Dál gCais were becoming powerful in the 10th century, with Mahon and his brother Brian Bóruma taking the throne in Munster from the Eóganachta; claiming ancient kinship with their rivals would have boosted their legitimacy.
It is claimed by current scholarship that the Dál gCais were instead a branch of the Déisi Muman. The Déisi Muman held a vassal kingship in Munster under the Eóganachta, significant in scope, consisting of what is today Waterford and its environs. As time went on branches also emerged around the River Shannon, as part of the Déisi Muman moved north-westerly between the 5th and early 8th century; they were called the Déisi Deiscirt and the Déisi Tuisceart. It is from later, more northerly branch, which the Dál gCais are said to ultimately find their true ancestors. The first recorded mention of their adoption of the new name Dál gCais specifically is in the Annals of Inisfallen for the year 934, which records the death of their king Rebachán mac Mothlai.
The Déisi Muman themselves are subject of The Expulsion of the Déisi epic in the Cycles of the Kings, which is set during the time that Cormac Ulfada was High King of Ireland. The story describes the expulsion of the Dal Fiachrach Suighe; kinsmen of the Connachta and descendants of Fedlimid Rechtmar; from Tara, coming to settle in Munster after many battles. Upon becoming the Déisi Muman, one branch then sailed across to Britain in the 4th century, coming to rule Dyfed. Their presence in Britain may have been initially supported by Magnus Maximus, Roman Emperor, as part of a policy of backing Gaelic vassals to be seafaring defenders of the shores of Britain facing the Irish Sea from pirates. Eoin MacNeill has pointed out that they were not the only Irish colony in the area, with the Uí Liatháin also powerful.
Ascent to the High Kingship of Ireland
The adoption of the name Dál gCais and the ascent of the group to greater power, began to take place during the 10th century with internal political transition. With the death of Rebachán mac Mothlai, the leadership of the Déisi Tuisceart shifted from the Uí Aengusa kindred to their junior relatives the Uí Thairdelbaig. It was during the time of Kennedy, who styled himself King of Thomond, that the Dál gCais began to challenge the Eóganachta; though Kennedy was defeated at the Battle of Gort Rotacháin by Cellach Caisil, King of Munster in 944. The actual reason for this sudden surge has been much debated and one frequently discussed thesis is that it was a political scheme of the Uí Néill, intending to use the Dál gCais as proxies to further weaken the power of the Eóganachta.
Kennedy's children built on their father's achievements. His daughter Órlaith became Queen consort of Ireland, after she married Donagh Donn, a High King of Ireland from the southern branch of the Uí Néill. Mahon became the first Dál gCais to gain the kingship of Munster, after he seized the Rock of Cashel from Molloy of the Eóganachta. Leading up to this he had defeated the Norse under Ivar of Limerick at the Battle of Sulcoit in 968. After Mahon was captured by Donovan in 976 and murdered by Molloy, the Eóganachta returned to the throne at Cashel for two years, but Mahon's younger brother Brian Bóruma, a seasoned military man from the early campaigns, would desire vengeance.
A campaign in 977-78 led to the defeat and death of Ivar, with an engagement at Scattery Island being the most significant. Brian retained the formerly Norse Limerick for its trading power and naval strength. The Dál gCais took back Munster at Belach Lechta the same year, killing Molloy in the process. Ambition saw Brian look next to the territories of Malachy II, High King of Ireland. A closely contested war of 15 years ensued, with the naval ability of the Dál gCais paying off as a truce was called by Malachy in 997, recognising Brian's overlordship of Leath Moga. They became allies against the Norse Dublin and the Laigin who under Máel Mórda, King of Leinster had risen against Brian's claims. The latter were subdued at Glenmama in 999, before rebelling again in 1014 at Clontarf where Norse power in Ireland was finally broken, though Brian died in the process. In the interim, Malachy had passed the High Kingship to Brian in 1002 and he built strong Christian links to Armagh.
After the death of Brian, his two established surviving sons; Donagh and Teague; struggled in an internal Dál gCais rivalry for dominion. While Donagh was High King, many other Irish kings allied against him, including Leinster, Connacht, and Ulster. Deposed in 1063, he fled to Rome, with some sources claiming he granted Pope Urban II the Irish crown, this is controversial, however.[note 1] Teague's son Turlough took up the reins in a lasting alliance with the powerful Dermot Kinsella, King of Leinster. Not a military leader, Turlough was instead a capable politician, the Cogad Gáedel re Gallaib glorifying Brian's feats would be authored during his lifetime. Turlough's son Murtagh would be the last High King from the Dál gCais of the medieval period, reigning between 1101–19. Murtagh attempted to make the Irish kingship more along the lines of European monarchies and was involved in foreign affairs (allying with Arnulf de Montgomery in the Welsh Marches against Henry I, King of England), trying to extend Irish influence beyond internal rivalries.
Septs and kindreds
The septs of the Dál gCais developed over time, with new ones breaking off to form separate surnames at different times, but all claiming to share the same paternal line (with a few biological exceptions along the way due to adoption or extra-marital issue). Their eponymous founder Cas had several sons; two of them gave their names to the Uí Bloid and Uí Caisin kindreds, another founded the Ui Fearmaic. As the proto-Dál gCais moved up into what is today East Clare, these became associated with rooted tribal areas, but were themselves internally divided into any other septs.
The senior line descended from Cas' first son Bloid and they provided the Kings of Thomond. Initially the leaders of the tribe were a sept known as the Uí Aengusa from which descends O'Curry, O'Cormacan and O'Seasnain. However, during the 10th century, this passed to the junior Uí Thairdelbaig. It is this kindred which would furnish the High Kings of Ireland and the Kings of Thomond including Brian Bóruma. From the Uí Thairdelbaig came O'Brien, O'Kennedy (who were Kings of Ormond), MacConsidine, MacMahon, O'Reagan, MacLysaght, O'Kelleher, Boland, Cramer, Kearney, O'Casey, Power, Twomey, Eustace, Ahearne, MacGrath, Quick, O'Meara, Scanlan, MacArthur, Cosgrave, O'Hogan, Lonergan and others. O'Noonan and Coombe are other notable Uí Bloid descendants. A younger brother of Carthann Fionn (who both the Uí Thairdelbaig and Uí Aengusa derive) named Brennan Ban stands at the head of the genealogies for the O'Brennan, Glinn, Muldowney and O'Hurley septs.
Although a junior line, the Uí Caisin continued to have a prominent role and the leader of their kindred in Thomond were the MacNamara, who as Lords of Clancullen, were the second most powerful family after the O'Brien. Other families descended from the branch of Carthann (son of Caisin) include Harley, Flood, Torrens, Stoney, Hickey, O'Hay, Clancy, Neylon and Flattery. Carthann had brothers named Eocha and Sineall from whom descends the O'Grady, Tubridy, Hartigan, Durkin, Killeen and Hogg. In addition to this, there are the Ui Fearmaic who claim to descend from Aengus Cinathrach, a brother of Caisin and Bloid. This kindred included the O'Dea as leaders, as well as the O'Quin, O'Griffin / O'Griffey (chieftains of Cineal Cuallachta), O'Heffernan, Kielty and Perkin. 
Within the traditional Gaelic culture of Ireland, society rested on the pillars of the tribal nobility, bardic poet historians and priests. Different families had different roles to play and in many cases, this was a hereditary role. However, the nature of this system, known as tanistry was aristocratic ("rule by the best") in the truest sense, in that if the tribe thought a younger male member of the family was more suitable to succeed to a role than an older sibling, then they could. The Norman and wider European concept of strict primogeniture was not completely adopted until after some of the families joined the peerage of Ireland.
The most powerful Dalcassian family of the hereditary Gaelic nobility were the O'Brien (Kings of Thomond), followed by MacNamara (Lords of Clann Cuilean), O'Kennedy (Kings of Ormond), MacMahon (Lords of Corca Baiscinn), O'Grady (Lords of Cinél Dongaile) and O'Dea (Lords of Ui Fearmaic). Some of these families later joined the peerage of Ireland after the surrender and regrant to the Tudors during the 16th century. The O'Brien was initially Earls of Thomond, but later became Barons Inchiquin which they hold to this day. The O'Grady was Viscounts Guillamore, while the O'Quins became Earls of Dunraven. A branch of the MacMahon family became Marquis de MacMahon d'Eguilly in the Kingdom of France, later raised to Dukes of Magenta under Emperor Napoleon III.
The Clancy sept was the hereditary Brehons of Thomond and held a very powerful position when it came to the law in the kingdom. Even after the end of the Gaelic order, they continued to play a role, providing a High Sheriff of Clare in the form of Boetius Clancy. Famously participating in the Contention of the Bards in support of the honour of the tribe, the MacBrody sept were the principal poets and historians of the Dál gCais over the course of centuries. The O'Hickey and Neylon sept would serve as hereditary physicians to the Dalcassians of Thomond. After the Norman Butler dynasty took Ormond, the Dalcassian sept of O'Meara became their hereditary physicians, this line included Barry Edward O'Meara, who was with Emperor Napoleon I in exile at St. Helena.
The Dál gCais polity up until the 10th century was approximately co-terminus with modern East Clare and exercised a large degree of regional autonomy from the Eóganachta Kings of Munster, and were powerful enough to kill the King of Cashel in battle in 713. The earliest Kings were derived from the Uí Oengusso kindred (descendents of Oengus, senior son of Carthann Finn who is said to be the first King of Dál gCais). On the death of Reabacán Mac Mothla in 934 the Kingship passed to the junior branch of Uí Toirdhealbhach descended from Eochaidh Bailldearg, another son of Carthann and the power of the Dál gCais began to expand greatly. Cinnéidigh was the first Dalcassian King to lead an army beyond his own territory and was acknowledged as King of Thomond by his death. His son Mathgamain built on these achievements, capturing Cashel and becoming King of Munster. The best-known member of this dynasty, Brian Boru, took over after his brother Mathgamain's death, reclaimed the Munster kingship and eventually succeeded in establishing himself as High King of Ireland before his famous death in the Battle of Clontarf. The Dál gCais under Brian's descendents, the Ua Briain would provide a further three High Kings of Ireland and exercised supremacy in Munster until Tairrdelbach Ua Conchobair, taking advantage of war between brothers Diarmait and former High-King Muircheartach, invaded Munster and split it in two in the Treaty of Glanmire (1118) granting Thomond to the sons of Diarmait Ua Briain and Desmond to the leading sept of the dispossessed Eoganacht, the Mac Cárthaigh dynasty. After the death of Domnall Mór Ua Briain, a claimant to the Kingship of Munster, they further retreated beyond the Shannon into the area of modern County Clare in the wake of the Norman Invasion. In 1276 King Edward II granted all of Thomond to Thomas de Clare, taking advantage of the feuding between Clann Taidhg and Clann Briain (whom de Clare supported). The de Clares failed in conquering Thomond and were decisively defeated in the Battle of Dysert O'Dea in 1318, thus the Kingdom of Thomond remained outside of foreign control for a further 200 years. In 1543 Murchadh Carrach Ó Briain, under pressure from the impending Tudor conquest, agreed to surrender his Gaelic Royalty to King Henry VIII and accepted the titles Earl of Thomond and Baron Inchiquin. At his death in 1551 the Earldom passed to his nephew Donough by special remainder and the title Baron Inchiquin passed to his male heirs through his son Dermot. The Earldom went extinct at the death of Henry O'Brien, 8th Earl of Thomond, the next heir would have been a descendant of Daniel O'Brien, 3rd Viscount Clare who was attainded in 1691, so the title became forfeit. However, Charles O'Brien, 6th Viscount Clare, a Jacobite exile used the title Earl of Thomond, as did his son, who died childless in 1774. At the death of James O'Brien, 3rd Marquess of Thomond, the title Baron Inchiquin passed to a distant cousin and descendent of Murrough, Sir Lucius O'Brien, 5th Baronet and was passed down to his descendents.
- = King of Dál gCais
- = King of Thomond
- = Baron Inchiquin
- =Viscount Clare
- =Earl of Thomond, Earl of Inchiquin
- =Marquess of Thomond
A higher Kingship title which is mutually inclusive with a lower one within the dynasty are not given overlapping dates for the simplicity of the chart.
|List of Kings (and later heads) of the Dál gCais|
- AI1021.2 Mael Muire Ua Gébennaig, eminent priest of Dál Cais, rested.
- Donagh certainly fled to Rome and was buried at the Basilica di Santo Stefano al Monte Celio. The stories about his time there are recorded by Geoffrey Keating in the 17th century, some with skepticism. The story was used in the 19th century as a potential explanation for Laudabiliter.
- Most information about the relationship between septs and their genealogical root can be found in John O'Hart's Irish pedigrees; or, The origin and stem of the Irish nation, where he worked from 17th century genealogists Cú Choigcríche Ó Cléirigh and Dubhaltach Mac Fhirbhisigh, as well as the Annals of the Four Masters.
- Reabacán mac Mothla is the only king listed for whom no precise pedigree survives. He is included in a list of kings said to be descended from Óengus and is therefore determined to be of the Uí Óengussa kindred but little else is known on his background. On his 934 death he is noted in the Annals as being both King of the Dal gCais (the earliest extant usage of this dynastic name) and Abbot of Tuaim Gréine.
- as per O'Harts Pedigrees
- "Coat of Arms". The O'Brien Clan. 8 March 2011. Archived from the original on 3 March 2012.
- The Tribe of Cas (26 August 2011). "Pedigree of MacMahon, Lords of Corca Baisgin, County Clare".
- Family History Ireland (26 August 2011). "Marshal MacMahon and the Ottomans".
- Family Steps by Leanne Chilver (29 May 2012). "Kennedy Origins Story".
- Clan O'Reagan (29 May 2012). "Reagan Presidential Memorial".
- Koch 2006, p. 554.
- Duffy 2004, p. 121.
- Davies 1994, p. 52.
- Rynne 1967, p. 230.
- "Dál gCais or The Dalcassians of Thomond". DalcassianSept.com. 12 November 2008. Archived from the original on 8 September 2010.
- "Irish Pedigrees, O'Brien". DalcassianSept.com. 12 November 2008. Archived from the original on 19 September 2010.
- "A Set of Distinctive Marker Values Defines a Y-STR Signature for Gaelic Dalcassian Families". JOGG.info. 7 July 2011.
- "The Kingdom of Thomond". Clan MaConmara. 7 July 2012.
- "Irish Pedigrees, MacNamara". DalcassianSept.com. 12 November 2008. Archived from the original on 19 September 2010.
- "Irish Pedigrees, O'Grady". DalcassianSept.com. 12 November 2008. Archived from the original on 19 September 2010.
- "Irish Pedigrees, Durkin". DalcassianSept.com. 12 November 2008. Archived from the original on 19 September 2010.
- "The Surname Ó Caiside". Brian Ó Cuiv. 12 November 2008. Archived from the original on 10 February 2012.
- "Ui Fearmaic - Irish Names and Surnames".
- "Irish Pedigrees, Quin". DalcassianSept.com. 12 November 2008. Archived from the original on 19 September 2010.
- O'Laughlin, Michael C. Families of County Clare Ireland. Irish Genealogical Foundation. ISBN 978-0940134980.
- "VII. Kineal Fearmaic".
- "The Dalcassian Knights, Gaelic Social Structure by Patrick M. O'Shea". DalcassianSept.com. 23 July 2012. Archived from the original on 30 October 2012. Retrieved 22 July 2012.
- James Frost (26 August 2011). "The History and Topography of the County of Clare, Part I. Topography of Thomond Chapter 7. Corcomroe".
- James Frost (26 August 2011). "The History and Topography of the County of Clare, Part I. Topography of Thomond Chapter 9. Ui Fearmaic; Gleann Omra; Ui Bracain; Ui Floinn; Ui Ronghaile".
- County Clare Library (26 August 2011). "MacBrody, MacBruaideadha".
- Moody 1991, p. 519.
- Bart Jaski, 'The (legendary) rise of Dál Cais', in: Seán Duffy (ed.), Medieval Dublin XVI: proceedings of Clontarf 1014–2014: national conference marking the millennium of the Battle of Clontarf (Dublin, 2017). 15–61., https://www.academia.edu/38265900/Bart_Jaski_The_legendary_rise_of_D%C3%A1l_Cais_in_Se%C3%A1n_Duffy_ed._Medieval_Dublin_XVI_proceedings_of_Clontarf_1014_2014_national_conference_marking_the_millennium_of_the_Battle_of_Clontarf_Dublin_2017_._15_61?source=swp_share
- The Normans in Thomond, Joe Power http://www.clarelibrary.ie/eolas/coclare/history/norman.htm
- Tadhg Ó Donnchadha,"An Leabhar Muimhneach", 1900, page 321-324, page 316, https://archive.org/details/leabharmuimhneac01odon/page/322, https://archive.org/details/leabharmuimhneac01odon/page/316
- Beatty, Aidan (4 March 2017). "Zionism and Irish Nationalism: Ideology and Identity on the Borders of Europe". The Journal of Imperial and Commonwealth History. 45 (2): 320. doi:10.1080/03086534.2017.1294237. ISSN 0308-6534.
- Davies, John (1994), A History of Wales, Penguin Books, ISBN 0-14-014581-8
- Duffy, Seán (2004), Medieval Ireland: An Encyclopedia, Routledge, ISBN 0-415-94052-4
- Koch, John (2006), Celtic Culture: A Historical Encyclopedia, ABC-CLIO, ISBN 1-85109-440-7
- Moody, Theodore William (1991), Early Modern Ireland: 1534–1691, Oxford University Press, ISBN 0198202423
- Rynne, Etienne (1967), North Munster Studies: Essays in Commemoration of Monsignor Michael Moloney, Thomond Archaeological Society
- Byrne, Francis John, Irish Kings and High-Kings. Four Courts Press. 2nd edition, 2001.
- MacLysaght, Edward, Irish Families: Their Names, Arms and Origins. Irish Academic Press. 4th edition, 1998.
- O'Brien, Barry, Munster at War. Cork: Mercier Press. 1971.
- O'Brien, Michael A., ed. (1962). Corpus Genealogiarum Hiberniae. 1. Kelleher, John V. (intro. in the reprints of 1976 and 2005). Dublin: DIAS. pp. 207–8, 235–45, 250 and 427. ISBN 0901282316. OCLC 56540733. Genealogies for the Dál Cais of Thomond
- Todd, James Henthorn (ed. and tr.), Cogadh Gaedhel re Gallaibh: The War of the Gaedhil with the Gaill Longmans. 1867.
- "Dál gCais – Church and Dynasty", Donncha Ó Corráin,
- Tribes and Territories of Northern Munster: Dál gCais
- The Tribe of Cas at DalcassianSept.com
- Irish Type III at IrishType3DNA.org
- R-L226 Project at Family Tree DNA