Diarmait mac Cerbaill
According to traditions, he was the last High King to follow the pagan rituals of inauguration, the ban-feis or marriage to goddess of the land.
The last High King to observe the ancient pagan Feis Temrach or Assembly of Tara which took place on Samhain every three years to pass or renew laws, approve annals and records.
This ambivalent character, together with the fact that he was the direct ancestor of the two most powerful dynasties of the Southern Uí Néill, made him an obvious figure for saga and legend.
The former are more prominent in the seventh century, but after the death of Cináed mac Írgalaig in 728 all the high-kings of the Southern Uí Néill come from the Clann Cholmáin except for a brief period between 944 and 956 when the king of Knowth, Congalach Cnogba, restored the high-kingship to the Brega line.
[4] It is remarkable that the Síl nÁedo Sláine and Clann Cholmáin derive their origin, not directly from Niall Noígiallach, but from his great-grandson Diarmait mac Cerbaill.
The petty Uí Néill kings of Cenél nArdgail traced their ancestry to an uncle of Diarmait's, but never won the high kingship.
In spite of his patronymic (Latinised by Adomnán as filius Cerbulis) the genealogical tradition says that his father's name was Fergus, nicknamed Cerrbél or 'crooked mouth'.
The previous King of Tara, according to the earliest lists, was Óengarb, an epithet meaning "extremely rough", presumed to refer to Diarmait's kinsman Tuathal Maelgarb.
[7] Following this defeat, Diarmait lost the battle of Cúil Uinsen to Áed mac Brénainn, king of Tethbae in Leinster.
He was killed in 565, probably at Ráith Bec in Mag Line (Moylinny, near Larne) in Ulster by Áed Dub mac Suibni, king of the Cruthin.
[8] According to the later Irish historians, Diarmait was followed as King of Tara by Domnall Ilchegalch and Forguss, sons of Muirchertach mac Ercae, of the Cenél nEógain.
[9] Adomnán of Iona, writing less than 150 years after Diarmait's death, describes him as "ordained by God's will as king of all Ireland."
[11] A poem, Mairg thochras fri cléirchib cell ("Woe to him who contends with the clergy of the churches") in the Book of Leinster, is ascribed to Diarmait.
Diarmuid dies a triple death: the roof beam of Tara has been recovered from the sea by Banbán and set in his hall, the shirt and mantle and ale and bacon are duly produced for Diarmait.
The Prophecy seemed so unlikely that Diarmuid scorned it, even when Banban invited him to a feast... Aedh Dubh was there and stabbed the High King with his spear.
Like tales are told of Muirchertach mac Ercae and Adomnán records that Columba prophesied a similar death, by wounding, falling and drowning, for Áed Dub.
Now this Aedh the Black had been a very bloodthirsty man, and cruelly murdered many persons, amongst others Diarmuid, son of Cerbul, by divine appointment king of all.
When such an ordination afterwards became known to the saint, he was deeply grieved, and in consequence forthwith pronounced this fearful sentence on the ill-fated Findchan and Aedh... And Aedh, thus irregularly ordained, shall return as a dog to his vomit, and be again a bloody murderer, until at length, pierced in the neck with a spear, he shall fall from a tree into the water and be drowned...
But Aedh the Black, a priest only in name, betaking himself again to his former evil doings, and being treacherously wounded with a spear, fell from the prow of a boat into a lake and was drowned.
From Adomnán's account it can be surmised that Áed was deposed, or abdicated, and spent time in Britain in a monastery before, presumably, returning to Ulster to try to regain his throne.
