Aided Diarmata
Supernatural features in Diarmait's reign are not limited to prose and verse works or to lives of saints. Even the Irish annals include a reference to druid fences being created at the battle of Cúl Dreimne. The main subject for later writers and poets however, was not Diarmait's life but his death.
Diarmait is told by Bec mac Dé that Áed Dub, Diarmait's foster-son, will be his killer. Accordingly, Diarmait banishes Áed Dub. Saint Ruadán gives the prophecy that Diarmait will be killed by the roof-beam of his hall at Tara. Diarmait has the beam cast into the sea. Diarmait then asks his druids to find the manner of his death, and they foretell that he will die a threefold death, by slaughter, drowning and burning, and that the signs of his death will be a shirt grown from a single seed of flax, a mantle made of wool from a single sheep, ale brewed from one seed of corn, and bacon from a sow which has never farrowed. On a circuit of Ireland, Diarmait comes to the hall of Banbán at Ráith Bec, and there the fate of which he was warned comes to pass. 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. Diarmait goes to leave Banbán's hall, but Áed Dub, waiting at the door, strikes him down and sets fire to the hall. Diarmait crawls into an ale vat to escape the flames and is duly killed by the falling roof beam. Thus, all the prophecies are fulfilled.
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.
Read more about this topic: Diarmait Mac Cerbaill