Maelgwn succeeded his father Cadwallon Lawhir as king of Gwynedd, about the year 517CE. He is presumed to be the king Maglocunos that Gildas accuses of being a most cruel character. Other Welsh saint lives seem to support Gildas, as it was recorded that he was rebuked by St. Padarn for certain injuries committed by him in Ceredigion and that he oppressed Tydecho, one of the Armorican saints, who had settled in his dominion. As is standard in these stories, the saint performs a miracle(s) which compels the perpetrator to make ample amends.
Maelgwn founded a College at Caergybi, and a Priory at Penmon, and also endowed Bangor, and raised it to a Bishopric. His reign was more powerful than most of those in this period. About the year 547-548CE, he died of the Vad Velen, or Yellow Pestilence, usually called the Yellow Plague of Rhos, which was said to have been caused by the number of unburied bodies of the slain that remained on that spot, and whoever went within the reach of the effluvia fell dead immediately.
To avoid the effects of this pestilence it is said that Maelgwn retired from his castle of Dyganwy, to the church of Llanrhos, where he hoped to remain, shut up in the sanctuary, safe from all danger; but being impelled by curiosity, he looked out through the keyhole of the door, and thereby caught the infection, thus fulfilling the prediction uttered by Taliesin,-
"A most strange creature will come,A traditional remembrance of this is preserved in the adage "Hun Maelgwn Gwynedd yn Eglwys Llanrbos," or as it is given in the "Annales Cambriae," published by the Record Commission, "Hir hun Maelgwn en Ilis Ros," as 'The long sleep of Maelgwn in the court of Rhos'.
From the sea marsh of Rhianedd,
As a punishment of iniquity,
On Maelgwn Gwynedd;
His hair and his teeth,
And his eyes being as gold;
And this will bring destruction
On Maelgwn Gwynedd."
This plague lasted from the year 547 to 562, and its ravages were fearful in the extreme. A Triad records it as one of the three direful maladies, and it is even employed as an image of horror in the compositions of the Bards. John Morris places the events and the plague 10 years earlier.
Maglocunus’s death is provided by the Annales Cambriae (Welsh Annals, c. 955CE):
Annales Cambriae, annus ciii (547CE)However, Vermaat has stated that he believes the entry itself is suspect, "copied from the earlier Chronicle of Ireland, which originally mentioned a list of Leinster names (not Maglocunus). The Welsh copyist may have had authority to substitute these names, but this is unknown to us. If not, the whole entry is false and any discussion bound to be useless." The 'mortalitas magna' is usually seen as the ‘Great Plague of Justinian’, which started in the east in 542CE, and which could easily have reached Britain by 547. The only problem is that Procopius (ca. 550) mentions this plague as a bubonic plague, whereas later tradition such as Welsh texts mention only a ‘Yellow Pestilence’ (Vad Velen). All references of this Vad Velen, come to us through Edward Williams, a.k.a. Iolo Morganwg (1745-1820), who, according to Ifor Williams, was 'the greatest forger of Welsh documents ever known. The damage that man has done! Maybe he was mad - let us be charitable'. Early MSS of the Mabinogion do not include these references to Vad Velen, but there are other sources that do. One is the Vita Teiliavi (Life of St. Teilo, 12th century), which confirms the death of Maelgwn in a Pestis Flava. A second MS of the Annales Cambriae mentions Hir hun Wailgun en llis Rhos (‘The long sleep of Maelgwn in the court of Rhos’). The ‘Yellow Pestilence’ is recorded for Ireland in the sixth century as the Cron Chonaill, which was mentioned by the Annals of Ulster for 548, which would fit the entry concerning Maglocunus. This disease was no plague, but might best be identified with ‘relapsing fever’, which occurs often together with a plague. Relapsing fever was common in Ireland together with famine, and its modern name is still fiabhras buidhe (yellow fever). If we consider that famine fever can spread from people lacking food to those with plenty of it (as it spreads through lice), we may have found a good candidate for the death of the king of Gwynedd."
Mortalitas magna, in qua pausat Mailcun rex Guenedotae
From De vita sancti Teiliavi (Saint Teilo):
Pestis autem illa flava vocabatur, eo quod flavos et exangues efficiebat
universos quos persequebatur.....Traxi[t] enim Mailconum regem Guenedotiae, delevit et patri[a]m suam...
[That plague is called yellow, because it makes everyone it attacks yellow and bloodless.... It dragged off Maelgun king of Guenedotia and weakened his people.]
