page_title: East Breifne
section_title: Norman invasion
hierarchical_section_title: East Breifne / Kingdom of Breifne c. 1120–1256 / Norman invasion
caption_attribution_description: English: Clogh Oughter Castle is situated on an island on Lough Oughter, County Cavan, Ireland
context_page_description: 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 came into existence following a protracted war between the ruling O'Rourke clan and the ascendant O'Reillys which culminated in the division of the kingdom in 1256. The Kingdom was ruled by the dynasty of the Ó Raghallaigh and lasted until the early 17th century.
context_section_description: 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.
  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.
  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.
caption: The initially Norman Cloughoughter Castle was captured & completed by the O'Reillys in 1233
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