Diarmaid Mac Murchadha, King of Leinster, is often considered to have been the most notorious traitor in Irish history.
After succeeding to the throne of his father, Enna, in 1126, Diarmaid Mac Murchadha faced a number of rivals who disputed his claim to the kingship. He established his authority by killing or blinding 17 rebel chieftains of northern Leinster in 1141. In 1167, he was deprived of his kingdom by the High King of Ireland – Ruaidri Ua Conchobair. The grounds for the dispossession were that Mac Murchadha had, in 1152, abducted Derbforgaill, the wife of the King of Breifne, Tiernan O’Rourke. A bitter feud ensued, and in 1166 Diarmaid was driven from Ireland to Wales and then England.
To recover his kingdom, Mac Murchadha solicited help from King Henry II of England. In return, Mac Murchadha pledged an oath of allegiance to Henry, who sent troops in support. King Henry II of England then granted the exiled ruler permission to enlist the aid of several Anglo-Norman lords of south Wales, notably, Richard de Clare, the 2nd Earl of Pembroke, (nicknamed Strongbow). Returning to Leinster in 1167 with an advance party of Anglo-Normans, Mac Murchadha established a foothold there.
As a further thanks for his reinstatement, Mac Murchadha’s daughter, Aoife, was married to Strongbow and promised the kingship of Leinster on Diarmaid’s death. (The marriage was imagined and painted in the Romantic style in 1854 by Daniel Maclise.) Henry II then mounted a larger second invasion in 1171 to ensure his control over Strongbow, resulting in the Lordship of Ireland.
Mac Murchadha was later known as Diarmaid na nGall (“Diarmaid of the Foreigners”) and died on this date in 1171 and was buried in Ferns Cathedral, where his grave can be seen in the outside graveyard.
Photo: Gravestone at Ferns Cathedral, Co Wexford. This is said to be the gravestone of Mac Murchadha.