Caer Wydyr: Seeing Beyond the Glass Fort

As I progress through ‘The Spoils of Annwn’ it is my growing intuition that imagistic links* suggest Taliesin is not referring to a series of different forts raided by Arthur and his men but to one otherworldly fortress by different names.

Under this tentative interpretation, verse four takes us from the theft of the cauldron and escape from Annwn back to the beginning of the action. Taliesin says:

‘I don’t rate the pathetic men involved with religious writings,
those who hadn’t seen Arthur’s feat beyond the Glass Fort:
six thousand men were standing on its wall;
it was hard to communicate with their watchman.’

Taliesin is mocking ‘pathetic men’ (monks) for being unable to see beyond Caer Wydyr: the Glass Fort. This is the fourth fortress named in the poem but, I intuit, the first to be approached.

In modern Welsh, gwydyr means glass. The image of the fort as glass: clear, see-through, near-invisible, is deeply evocative of its otherworld nature. Its walls, with room for six thousand men, are extensive.

It is possible to think of these glass walls as representative of the boundary between thisworld and Annwn. To penetrate beyond requires an invitation from Annwn’s deities, cunning, or a good deal of brute force.

Much speculation surrounds the incommunicative nature of the watchman. In other poems and stories such as ‘Arthur and the Porter’ and Culhwch and Olwen, the watchmen/gatekeepers are communicative. Questions must be answered and conditions met to enter the fortresses of otherworldly persons.

The watchman’s incommunicability has led some scholars to suggest he and perhaps the six thousand men on the walls are risen dead. In The Second Branch of The Mabinogion, dead Irishmen thrown into the Cauldron of Rebirth rise able to fight but unable to speak.

Another possibility is the guards are the spirits of Annwn who are ruled by Gwyn ap Nudd. They are perfectly able to speak: in The Life of St Collen, Gwyn’s watchman courteously invites St Collen into ‘the fairest castle he had ever beheld’.

The ominous silence of the watchman and six thousand men could stem from the fact three loads of warriors from Arthur’s warship have just landed outside their home, fully-armed, with their eyes glinting with lust for Annwn’s treasures.


Glass fortresses are a recurrent feature in Celtic literature and are often the abode of otherworldly rulers. This leads me to suspect there was once a deep, underlying mythos surrounding the Head of Annwn and his otherworldly fort which has gradually been lost.

A very close parallel with Caer Wydyr can be found in Nennius’ History of the Britons. Thirty ships of Spaniards sailing to Ireland find in the midst of the sea ‘a tower of glass, the summit of which was covered with men, to whom they often spoke, but received no answer.’ When they attack the tower, all but one of their ships are swallowed by the waves.

In The Life of St Gildas, Glastonbury is described as the Island of Glass. Caradog of Llancarfan says ‘Glastonia was of old called Ynisgutrin, and is still called so by the British inhabitants. Ynis in the British language is insula in Latin, and gutrin (made of glass).’

This is echoed by Gerald of Wales in Speculum Ecclesiae. Glastonbury ‘used to be called “Ynys Gutrin” in the Welsh language, that is the Island of Glass, no doubt from the glassy colour of the river which flows around it in the marshland.’

Glastonbury is the abode of Gwyn ap Nudd and Melwas who are both abductors of important female figures and riders of the famous water-horse ‘The Black of the Seas’**. Melwas keeps Gwenhwyfar imprisoned on the Island of Glass.

In Sir Orfeo, the Fairy King abducts Orfeo’s wife, Heurodis, and takes her to his crystal castle. Its vivid description provides clues to the appearance of Caer Wydyr:

‘Amid the land a castle tall
And rich and proud and wondrous high
Uprose, and all the outmost wall
Shone as crystal to the eye.
A hundred towers lit up the sky,
Of diamond all battled stout;
And buttresses rose up near by
Arched with red gold and broad about.

All the bonsour was carved in stone
With every beast and every wight,
And all within the castle shone
And sparkled with unearthly light.’


In The Four Branches of the Mabinogi, Will Parker suggests the imagery of ‘the Indigenous Underworld of Annwfn’ stems from the ‘memory of the riches of the Romano-British civilian zone’.

The Romans brought glass-making to Britain and it seems likely memories of their cosmopolitan ways of life, fine clothes, and wine fed into conceptions of Annwn, which later became known as Faery.

A fascinating blend of Brythonic and Roman influence can be found in the list of ‘The Thirteen Treasures of the Island of Britain’ ‘that were in the North’:
‘Drynwyn… the Sword of Rhydderch the Generous’, ‘The Hamper of Gwyddno Long-Shank’, ‘The Horn of Brân the Niggard’, ‘The Chariot of Morgan the Wealthy’, ‘The Halter of Clydno Eiddyn’, ‘The Knife of Llawfroedd the Horseman’, ‘The Cauldron of Dyrnwch the Giant’, ‘The Whetstone of Tudwal Tudglyd’, ‘The Coat of Padarn Red-Coat’, ‘The Vat and Dish of Rhygenydd the Cleric’, ‘The Chessboard of Gwenddolau son of Ceidio’ and ‘The Mantle of Arthur’.

All these treasures possess magical qualities which are suggestive of their otherworld origin. They are also of interest because in the marginalia of the list in Pen. 147 (1566) we find the story of how Myrddin managed to acquire them and retreat ‘to the Glass House’ (ty gwydyr).

The traditional location of Myrddin’s glass house is Bardsey Island. Patrick Ford says ‘In a version of… “Treasures of the Kings of Britain”… Mad Merlin took all these from the city called Caerlleon-on-Usk to the House of Glass in Bardsey Island’.

In Celtic Remains, Lewis Morris says ‘In Caerlleon on Usk there was a museum of rarities in King Arthur’s time, which Myrddin ap Morfran, the Caledonian, upon the destruction of that place, carried with him to a house of glass on the Isle of Enlli or Bardsey…

This house of glass, it seems, was the museum where they kept their curiosities to be seen by everybody, but not handled; and it is possible Myrddin, who is said to live in it, was the keeper of their museum at the time’.

The shift from treasures used by their owners (some stolen by Arthur: Gwyddno’s Hamper and Dyrnwch’s cauldron) to their placing in a glass museum as relics is an interesting one, which reflects that they have fallen out of use and become part of our cultural heritage.

It also shows we have become cut off from their magic. As Christianity replaced Romano-British paganism, the doors to Annwn were sealed. Mad Myrddin became the uncommunicative watchman of the glass walls.

Caer Wydyr and its people have been forgotten and we have since then built our own Glass Fortresses: Crystal Palaces, Arcades, department stores, shopping malls, and stocked them full of the treasures of thisworld.


The Crystal Palace, London,  Great Exhibition 1851, Wikipedia Commons

P1150490 - Copy

Yet the call returns to journey to Annwn, to see beyond the Glass Fort to the feats of Arthur, to their consequences reflected like mirror images in the years between then and now.

*Caer Vedwit and Caer Rigor are described as having four quarters/corners/turrets/pinnacles/ peaks and Caer Vandwy is referred to as the Fortress of God’s Peak. The sea beats around the turrets/pinnacles of Caer Siddi.
**In Culhwch and Olwen the only horse Gwyn can hunt Twrch Trwyth ‘King of Boars’ with is Du y Moroedd ‘The Black of the Seas’. In the opening lines of The Dialogue of Melwas and Gwenhyfer, Melwas introduces his horse before himself

‘Black is my steed and brave beneath me
No water will make him fear
And no man will make him swerve.’

It is notable that in The Conversation of Gwyn ap Nudd and Gwyddno Garanhir, Gwyn also introduces his horse (although here it is Carngrwn) first.

7 thoughts on “Caer Wydyr: Seeing Beyond the Glass Fort

  1. Brian Taylor says:

    I had no idea that poor Myrddin ended up as a museum attendant! Is there any connection, apart from a relationship with magic, that links this fragment of story with those about his retreat into the wild wood?

    • lornasmithers says:

      Yes, Myrddin fought for Gwenddolau at Arfderydd and Gwenddolau was the owner of one of the 13 treasures – a chessboard that played itself. When he’s taking refuge in Celyddon, Myrddin hides from Rhydderch Hael, the owner of another treasure – a white-hilted sword that burst into flames when touched by a nobleman. Connect this up with Gwyn attending Gwenddolau’s death as a psychopomp you find that Gwyn also attended the deaths of two more owners of treasures – Bran Galed who had an endless drinking and Gwyddno Garanhir who had a magic hamper. It seems both Gwyn and Myrddin had a role to play as the Old North fell – gathering the souls of its warriors and taking their treasures back to the otherworld. The museum bit feels like a much later addition!

  2. greg says:

    Your view of all the forts in the fortress as one fort accords with my own, or at least that it is the nature of such an otherworld fortress that there will be many outward appearances depending on who approaches and for what purpose. They have also been seen as stages on an initiatory journey, which is useful in some ways but tends to place it in the personal space rather than in the realm of numinous manifestation.

    The castle in Sir Orfeo is even more suggestively portrayed in the 13th century text where the line about it being like crystal is: “Was cleer and shined as crystal”. When there are recurrent images of this sort, as you outline in your various examples, there does seem to be a persistent outcropping of something deep the significance of which deserves further exploration.

    On the importance of horses, do you know the references in Tacitus where he says that the northern European tribes kepd horses in sacred groves specifically and solely for divination?

    • lornasmithers says:

      It’s interesting to hear that my developing ideas about the names of the fort being for one that manifests in many ways accords with your own. Thanks for sharing that. I *must* get round to reading those other Orfeos at some point! I was unaware of the Tacitus reference but recurrently I have come across references to how important horses were to the Celts. In medieval Welsh poetry they seem to be honoured above all other animals and near inseparable from their owners. How much this had to do with a genuine love of horses and of horses as a symbol of status and wealth I’m not sure and guess it would have varied from individual to individual. Any ideas about how the horse divination worked?

      • greg says:

        Tacitus on horse divination:
        “In common with other nations, the Germans are acquainted with the practice of auguring from the notes and flight of birds; but it is peculiar to them to derive admonitions and presages from horses also. Certain of these animals, milk-white, and untouched by earthly labour, are pastured at the public expense in the sacred woods and groves. These, yoked to a consecrated chariot, are accompanied by the priest, and king, or chief person of the community, who attentively observe their manner of neighing and snorting; and no kind of augury is more credited, not only among the populace, but among the nobles and priests. For the latter consider themselves as the ministers of the gods, and the horses, as privy to the divine will.”

        From Germania

  3. Nimue Brown says:

    I am pout in mind of the kennings as a way of naming things, and the multiplicity of names that comes with said approach. it’s a more poetic way of walking about things. which would make sense in this context. And the speaking obliquely of things of power and importance so as not to hand over vital insights to the other side…

  4. G. B. says:

    There are two ‘fortresses’ mentioned in The Spoils of Annwn. One was indeed an authentic fortress, having been a stone fort of pre-historic origin and hence windowless. The other was a 12th century Cistercian monastery, no longer existing on its known site, but its design would have resembled that of Duiske Abbey (1204 AD) at Graiguenamanagh, Co. Kilkenny, or Strata Florida Abbey (1164 AD) in Wales, both of which were built to the same plan and both well lit by windows. In that context the gaelic poet used some Irish name alluding to its glass or brightness, which has been translated to Welsh as Caer Wydyr and later to English as the Glass Fortress. The first Cistercian monastery in Ireland was founded at Mellifont in 1142.

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