| Conflict: | Battle of Dysert O'Dea |
| Partof: | the Bruce campaign in Ireland |
| Date: | 10 May 1318 |
| Place: | O'Dea Castle near Corofin, County Clare |
| Result: | Gaelic victory |
| Commander1: | Conchobhar Ó Deághaidh |
| Commander2: | Lord Thomond† |
| Strength1: | ? |
| Strength2: | ? |
| Casualties1: | 80 dead |
| Casualties2: | 400–500 dead |
The Battle of Dysert O'Dea took place on 10 May 1318 at Dysert O'Dea near Corofin, Ireland. It was part of the Bruce campaign in Ireland. The Norman Richard de Clare attacked the Gaelic Irish chieftain Conchobhar Ó Deághaidh, chief of the Cineal Fearmaic and ally of Muircheartach Ó Briain, but he was defeated.
The Bruce invasion of Ireland enabled the outbreak of a number of small wars that had little, if anything, pertaining to the Scots. Perhaps the most notable was the battle at Dysert O'Dea which erupted in Brian Boru's old Kingdom of Thomond in 1318.
Two factions of the O'Brien clan had been fighting for generations for supremacy in Thomond. Murtough O'Brien, the descendant of Thurlough O'Brien was the rightful King of Thomond. A challenger appeared in the form of Mahon O'Brien, allied with the opposing faction of the family, which paid its homage to Brian O'Brien. This side of the family was allied with the powerful Anglo-Norman Richard de Clare, a relative of Strongbow. De Clare ruled over much of western Ireland from his castle at Bunratty, yet the English respected Thomond as a sovereign state and remained outside its borders. However, de Clare's alliance with Mahon O'Brien provided an excuse to invade Thomond. His pale Englishmen would meet in a pitched battle against Murtough's Irish in the Battle of Dysert O'Dea.[1]
During this time, Donnchadh, an ally of de Clare, was overwhelmingly defeated in the Battle of Lough Raska near Corcomruadh Abbey.
When news arrived of his allies' defeat at Corcomruadh, Richard de Clare decided to attack the Gaelic stronghold at Dysert O'Dea. His troops arrived at Ruan on the morning of 10 May 1318, and were divided into three columns. The first division was headed by de Clare's son and marched northwards to Tullach O'Dea in an effort to cut off any help which might arrive from O'Connor of Ennistymon. The second column travelled southwards towards Magowna to quell any support from that direction. The third division was commanded by de Clare himself and marched westwards towards Dysert O'Dea, the home of Conor O'Dea. O'Dea intentionally made his forces look few in number, for some time fighting in retreat, and when de Clare charged for an attack the Anglo-Normans were ambushed. Richard de Clare was felled by an axe and his son was killed by a Feilim O'Connor.[2] The O'Deas were reinforced by the O'Connors and later the O'Briens, who turned the tide of a potentially unpredictable battle[3] [4] along with further decisive assistance from the O'Hehir and MacNamaras; and the English were soon defeated. Following their victory, the Irish marched back to the de Clare settlement, only to find that de Clare's wife had set it aflame, including Bunratty Castle, and had returned to England.
Over eighty Englishmen of noble birth and many foot soldiers were killed in the battle. The Kingdom of Thomond remained beyond foreign control for over two hundred years, until 1570.[5]