4. A favourite myth of this deity.
Perfect is my chair in Caer Siddi
Sickness and old age afflict not those within it
Manawyd and Pryderi know it…
Save seven, none survived.
The fleet which sailed to Ireland was so thick with masts that it appeared as though a forest was moving on the waves. Yet, of all those who sailed, only seven returned to the Island of the Mighty. Manawydan. Pryderi. Taliesin. Glifieu Eil Taran. Ynawg. Gruddieu son of Muriel. Heilyn son of Gwyn the Old.
They returned with the head of Bendigeidfran, struck from his poisoned body at his own command. It was a wondrous thing: it remained uncorrupted, as he had foretold, and kept them excellent company as they journeyed through Harlech and Gwales towards London, to bury it beneath the White Hill.
On reaching Harlech, the seven feasted, with the head of Bendigeidfran at their table. The three birds of Rhiannon rose up and surrounded them with song, a song so sweet that it could wake the dead and lull the living to a death-like sleep. Not one of them would stir while those birds were singing. They feasted for seven years, and when the singing stopped, they set out for Gwales, rejuvenated.
The island fort of Gwales was set high above the sea, a beautiful palace with a kingly hall. Two of its doors lay open to them, and a third was closed.
‘There,’ said Manawydan to his six companions, ‘is the door we must not open.’
That night they feasted again, and every night thereafter. For eighty years they remained in that hall, lacking nothing, feeling nothing of their grief, knowing nothing of the time that passed them by. And the head of Bendigeidfran feasted with them, as good company as it had ever been when on his body. But at the end of eighty years, Heilyn son of Gwyn the Old grew restless, and began to look towards the door that had not yet been opened.
‘Shame on my beard,’ he said, ‘if I do not open that door and find out what lies beyond.’
So he opened it, and looked outside, at the silted waters of Aber Henvelen flowing westwards towards the setting sun, and in that moment, he and every other person in the palace knew that they could stay no longer. They took the head of Bendigeidfran and set out for London, with all the burden of their grief to spur them on.
The Assembly of the Wondrous head is one of the most haunting episodes in the Mabinogi, for me. There has been a lot of debate over the precise physical location of the island of Gwales, and in my retelling I hint at its possible real-world counterparts: Aber Henvelen is sometimes taken to mean the Bristol Channel, and the door that must not be opened faces onto Cornwall. But, of course, this episode does not take place in our world.
Will Parker has a lot to say about the tradition of the island otherworld in Celtic literature, which was described by Roman writers as ‘a significant aspect of the belief system of the native populations of Gaul and Britain.’ Remarkably, this tradition continued to flourish on both sides of the Irish Sea after the arrival of Christianity: ‘[with] roots in the pagan past, they also received an important lease of life by being assimilated into the patristic traditions of the peregrinato, and Christian visions of the prelapserian paradise.’ Parker places this story in the context of The Voyage of Bran, and the otherworldly visions described in the poems of the School of Taliesin – particularly the description of Caer Siddi, which seems to be a variation on the Irish ‘sidhe‘. As he notes, the otherworld ‘was sometimes depicted as an underground realm, sometimes as an island in the sea, sometimes in a sub-aquatic location’. It is characterised by spatial and temporal distortion, and the psychic element of the otherworld experience is at least as important as its physical location. Otherworldly islands abound in folkloric tales relating to Manannán, and I hope to explore them in greater depth (pun intended?) at some point in the future on this blog. But the Assembly of the Wondrous Head has a strange and magical resonance, capturing the potent mix of pagan and magical Christian beliefs which provide us with our spiritual inheritance as British druids, while also expressing a Celtic world which was fast disappearing; first under Roman conquest, and then under Anglo-Norman rule:
The Second Branch as a whole is shot through with a potent combination of wonder and nostalgic yearning, that distinctive emotion the Welsh know as hiraeth. A fitting mood, perhaps, for the contemplation of the splendour of a distant and irretrievable past, the memories of which were on the point of fading from the terrestrial map of geopolitical validity into the celestial distance of myth, like the melting of the sunset over the Western Sea. 
 Golychaf i Gulwyd – my own translation, drawing heavily on Kristoffer Hughes’ research for the 13th Mt Haemus lecture: http://www.druidry.org/events-projects/mount-haemus-award/thirteenth-mt-haemus-lecture
 Will Parker, http://www.mabinogi.net/