In Irish mythology, Mesgegra (Mess-gegra, Mes Gegra, Mes Gedra) was king of Leinster during the events of the Ulster Cycle, and was also the brother of Mac Da Thó aka Mes Róidia in The Tale of Mac Da Thó's Pig.
Mesgegra was killed by the Ulster warrior Conall Cernach, who preserved Mesgegra's brain in lime as trophy. But the brain-ball was stolen by the Conacht warrior Cet mac Mágach who shot it at the Ulster king Conchobar Mac Nessa and lodged in his head, killing him seven years later, thus fulfilling the prophecy that Mesgegra would somehow avenge his own death.
Name
Mes-gegra is mentioned in Cormac's glossary, only to state that Mes signifies 'edge' or 'blade'.
Mesgegra (Mess-gegra) was king of Leinster (North Leinster), whose parents were deaf and mute; his brother was named Mes-Róidia (var. Mes roida).
To Leinster arrived the Ulster poet Athirne, who had been dispatched from his king Conchobar mac Nessa and was making circuit around Ireland to exact ruthless demands of precious jewels, or women, or even an eye, on pain of receiving the poet's invective and dishonor. The poet intended to goad the Leinstermen into killing him, thereby causing war between Leinster and Ulster, so he named an impossible bribe, a lost buried heirloom jewel, but that was fortuitously found and given him.
Mesgegra yielded his wife Buan to the poet for a night, but did not have his wife taken away afterwards, although he had to make a binding promise that she would be given to whichever Ulsterman arrived bearing Mesgegra's head. The poet then carried away him 150 wives of Leinstermen, so that the Leinster army did give pursuit, and clashed with the Ulster army. The ensuing battle, the Siege of Howth, was a bloody stalemate which ceased when Leinster retreated and erected a red wall as barrier, which Ulstermen were forbidden from crossing (due to a geis).
Mesgegra was incautiously tarrying with just his gillie in his company at a spot called Cassán Chlóinta (Path of Clane), where a strange incident unfolds. A giant nut larger than a man's head floats down the stream, which Mesgegra takes and halves with a knife. The gillie wakes up claiming to have had an evil vision, and asks if his half of the nut was saved, then slashes off the king's hand without properly confirming. Learning his mistake afterwards, the gillie commits suicide. Mesgegra's brain was later stolen by Cet Mat Matach) of Connacht as it was prophesied that Mesgegra would eventually avenge himself even in death.
It is worth mentioning that Cet had been outdone and shamed by Connal (and the Connachtsmen shamed by the Ulstermen in general by Connal's administration of the curadmír or "Champion's Portion" in the Scéla Muicce Meicc Dá Thó), is identified as a brother of Mesgegera the king.
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;Bibliography
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