The Kingdom of East Breifne or Breifne O'Reilly (; , ) was an historic kingdom of Ireland roughly corresponding to County Cavan that existed from 1256 to 1607. It took its present boundaries in 1579 when East Breifne was renamed Cavan, after Cavan town, and shired into Ulster.
Originally part of the older Kingdom of Breifne, East Breifne emerged following a protracted war between the ruling O'Rourke clan and the ascendant O'Reillys, culminating in the kingdom's division in 1256. The Kingdom was ruled by the Ó Raghallaigh (O'Reilly) dynasty and lasted until the early 17th century.
Origins and etymology The area of modern-day east County Cavan has been inhabited for over 5,000 years. The O'Reilly are descendant from a kin-group known as Uí Briúin, who settled the east Breifne area in the eighth century AD. At some point they splintered off from the Uí Briúin sept and became known as Muintir-Maelmordha, named after their chief Maelmordha who lived in the 9th century.Parker, pp. 155 They did not assume a surname until the early 11th century when they became known as O Raghallaigh, from the chieftain Raghallach. They are believed to have arrived in what is now County Cavan in the 10th century. Muintir-Maelmordha first appear in the Irish annals as a clan ruling a small territory around Lough Ramor called Machaire Gailenga in 1126, at which point they are a vassal of the O'Rourkes.Simms, pp. 306
Kingdom of Breifne c. 1120–1256 Machaire Gailenga was annexed after the O'Reilly were defeated by the O'Rourkes and became a constituent clan within what was then known as the Kingdom of Bréifne and Conmaicne. King Tigernán Mór Ua Ruairc, who reigned from 1124 to 1172, was conquering eastward and it was under Tighernán Mór that the Kingdom of Breifne reached its greatest expanse, extending from Hill of Ward and Kells, County Meath to Drumcliff, County Sligo in the late 12th century. Tighernán Mór consolidated the eastern territories he had conquered through his marriage to Derbforgaill, daughter of the King of Meath.
There was great animosity between the subjugated O'Reillys and their O'Rourke overlords. Tighernán Mór went to war with King Diarmait Mac Murchada of Leinster in 1152 following Mac Murchada's abduction of Queen Derbforgaill, and his claim over land that was in Brefnian possession. Taking advantage of Breifne's preoccupation, chief Geofraidh O'Reilly launched an unsuccessful rebellion in 1154 and was banished from the kingdom following his defeat. In 1155 when Donnchad Ua Cerbaill king of Airgíalla was captured and imprisoned by Tighernán Mór, Geofraidh O'Reilly and his supporters ambushed the Brefnian guards and rescued Ua Cerbaill. O'Reilly was later captured and executed for this act of sedition.Simms, pp. 306
Norman invasion
Tighernán Mór formed a coalition with the High King, Ruaidrí Ua Conchobair, which ousted Mac Murchada in 1166. Mac Murchada fled to England and sought help from Henry II to aid him in reconquering his kingdom. This prompted the Norman invasion of Ireland in 1169. With Norman aid Mac Murchada retook Leinster, and set Kells, Breifne's easternmost outpost, ablaze. In 1170 Breifne was invaded and in the following years the kingdom was carved up by the Normans. O'Rourke power was weakened whilst the O'Reilly submitted to Mac Murchada and his Norman allies during the conquest.
Shortly after Mac Murchada's death in May 1171, most of the native Irish kingdoms waged war on his successor, Richard de Clare or "Strongbow". However, the O'Reilly allied themselves with the Normans as a way of breaking free of the O'Rourke. The division between the two clans is most apparent during the Siege of Dublin, when the O'Rourke king is encamped outside the city with his Gaelic allies, and the O'Reilly king is inside aligned with Strongbow and his council.
During parley in 1172 at Trim, Tighernán Mór was betrayed and killed by Hugh de Lacy, Lord of Meath, throwing the O'Rourke dynasty into chaos. The instability and wars of succession between the various branches of the O'Rourke sept weakened their hold over the territory of Breifne even further. With the help of de Lacy, the O'Rourkes were driven back and expelled from O'Reilly land. Good relations between the O'Reilly and the Normans persisted until the early 13th century when they were soured by Hugh's two sons, Walter and William Gorm.Simms, pp. 307
The influence of the Normans in eastern Breifne was considerable and by 1211 they had established castles in Belturbet and Kilmore. King John of England took possession of the Lordship of Meath from the de Lacy family following Hugh's death, but it was returned to Hugh's son Walter de Lacy in 1215. Walter, William Gorm, and their Anglo-Norman forces began expanding into Breifne in an attempt to increase their influence to western Ulster. By 1220 de Lacy had taken control of most of the O'Reilly territory, including the stony island at Lough Oughter, where William Gorm began construction of a castle. Cathal O'Connor, King of Connacht, wrote to Henry III in 1224 informing him that the de Lacy family had not only seized Breifne from the O'Rourkes, but the Earldom of Ulster as well. Seeing that Walter had clearly overstepped his boundaries, Henry III sent an English force led by William Marshal to Ireland to put down de Lacy. The O'Reillys assisted Marshal in his campaign against de Lacy and, following a short siege, retook the castle at Lough Oughter, which they finished in 1233.Simms, pp. 308
During Marshal's punitive war in Ireland, chief Cathal O'Reilly, great-grandson of Geofraidh, exploited the power vacuum left by de Lacy to secure control of Breifne from his enemies. In 1226 he captured and demolished de Lacy's castle at Kilmore and raided into western Breifne, killing the O'Rourke king's son Aodh at Lough Allen. Cathal had set into motion the events which over the following 30 years would culminate in the dissolution of Breifne.
O'Reilly Rule 1230–1250
For his assistance in the campaign against de Lacy, Henry III issued a royal grant to the King of Connacht giving him overlordship of Breifne, a position which he delegated to his son Aedh. Naturally, this position was challenged by the O'Rourkes, who themselves were overlords of Breifne. Keen to usurp the power of the O'Rourkes, Aedh entered into an alliance with their most intractable enemy, the O'Reillys. The O'Rourkes now had the O'Reillys attacking from the east and Connacht attacking from the west.
Evidently alarmed by the prospect of a "lesser clan" rising up and seizing control of the kingdom, Domnhall O'Donnell, King of Tyrconnell, sailed south across Lough Erne and into Lough Oughter, where he destroyed Cathal O'Reilly's home, abducting his wife Cacht, and killing his favourite horse. Cathal survived and was able to put the traumatic event behind him, even agreeing a peace with Tyrconnell shortly afterwards.Simms, pp. 310
With Connacht's help, the O'Reillys had usurped control of Breifne by the early 1230s. Cathal O'Reilly ruled as king from the east of the kingdom and Cúchonnacht O'Reilly, Connacht's foremost general and close ally of King Felim O'Conor, had militarily taken control of western Breifne and expelled the O'Rourke leaders. In 1233 William Gorm de Lacy, having received a royal pardon for his overseas service, attempted to retake Breifne with a large force of English and Anglo-Irish soldiers. He was decisively defeated by Cathal and Cúchonnacht at Moin Crandchain near the Meath border, and died from his wounds.
Following the battle, eastern Breifne emerged relatively stable, but Cúchonnacht is mentioned numerous times in the annals suppressing what was effectively a guerilla warfare campaign against his usurpation of their rule by various O'Rourke nobles in western Breifne. In 1237 Richard Mór de Burgh ousted Felim O'Conor who turned to Cúchonnacht for aid. Cúchonnacht was able to raise an army from the men of western Breifne, illustrating that his grip on that half of the kingdom was relatively strong by this point. Cúchonnacht and Felim had remarkable success against the Anglo-Norman forces despite the latter's superior technology, such as chain armour.Simms, pp. 311
However, by 1239 and throughout the 1240s, the O'Reilly came into conflict with O'Conor. The king of Connacht was severely diminished and ruled only the area of modern-day County Roscommon, most of the province had fallen to de Burgh. The O'Reilly were now the most powerful players in the region and Cúchonnacht attempted to cement his dominance. Given his actions, Cúchonnacht was perhaps more powerful than Cathal at this point, despite the former holding no official office or title. The conflict between the two kingdoms came to a head when the battered O'Conor sept attempted to reassert the primacy it once had over Breifne.
In response to O'Conor's actions, the chiefs of the lesser clans of the area such as those at Moylurg and Muintir Eolais, traditionally vassals of the O'Conors and the O'Rourkes, were removed and replaced with puppet leaders by Cúchonnacht. He effectively ruled by decree and garnered a reputation as a tyrant. One such instance that provoked outrage across the province was an unscrupulous deal in 1242 in which Cúchonnacht supported the claim of Tadhg O'Conor, a rival claimant to Felim, on the condition that he, as king of Connacht, renounce all claims to Breifne. By the Autumn of 1242, when it had become apparent that Tadhg had garnered little support for his claim and was no longer of any use to Cúchonnacht, he was seized and imprisoned. In the spring of 1243, Cúchonnacht ordered the young prince to be blinded and castrated. This drove Felim to throw more support behind the O'Rourkes and their claim to Breifne.Simms, pp. 313, 314
Secession of East Breifne
The 1240s saw widespread conflict between the native Irish and the Normans, who were at this stage engaged in near constant war. De Burgh's advance forced Felim O'Conor to flee to Tyrconnell in 1249. There he met with King Brian Ua Néill of Tyrone and the deposed Conchobar O'Rourke of Breifne, and they formed a coalition against the Normans and their allies. While the O'Reilly joined Maurice FitzGerald, Justiciar of Ireland in his abortive march into Ulster, Ua Néill marched south and restored Felim O'Conor to his throne in Connacht.
From 1250 onwards western Breifne was wrested back from Cúchonnacht. In 1255 Breifne was raided three times by Ua Néill, and was invaded from the west by O'Conor and O'Rourke. Connacht declared Conchobar O'Rourke as King of Breifne, and gave Conchobar O'Reilly, Cathal's discontented son, the lesser position of Taoiseach. Cúchonnacht and his forces had been pushed out of the west. In 1256 Walter de Burgh raided into Connacht to devastate the country and relieve pressure on the O'Reillys who further north had ventured into western Breifne to retake control of the territory.
The two armies were meant to rendezvous at Lough Allen but the O'Reillys came under heavy attack and were forced to retreat. They were pursued northwards to Magh Slécht, where the Battle of Magh Slecht ensued. The O'Reilly and the O'Rourke suffered heavy losses, both Cúchonnacht and Cathal were slain in the battle, as were 14 other O'Reilly nobles. Connacht and the O'Rourke emerged victorious and O'Reilly power was shattered.
Relations between the O'Conor and the O'Reilly were extremely hostile and, following his victory at Magh Slecht, Aodh O'Conor, Prince of Connacht, was determined to continue to conquer into the east and bring all of Breifne under Connacht's control. This was briefly achieved following the inauguration of Conchobar O'Reilly, Aodh's ally, as head of the O'Reilly clan. However Conchobar died the following year and was succeeded by Matha O'Reilly, who immediately broke ties with Connacht.Parker, pp. 159