Mur y Castell is Llew Llaw Gyffes’s palace and seat of rule, placed on the confines of Ardudwy. First established as the home of a beloved ruler, it becomes a contested stronghold after Llew is attacked: Gronw Pebyr takes possession of the surrounding land, and Gwydion later leads an army there to restore Llew’s rights.

Setting and Rule

Math grants Llew the Cantrev of Dinodig after Llew’s marriage to Blodeuwedd, describing it as the best cantrev to hold. The territory is said to be called Eivionydd and Ardudwy in the narrator’s time. Within it, Llew makes his palace at Mur y Castell, on the border of Ardudwy, where he lives and reigns. Both the ruler and his sway are beloved by the people, establishing the palace initially as the centre of a settled and accepted authority.

Llew’s residence is also a point of connection to Math’s court: he travels from Mur y Castell to Caer Dathyl to visit Math. His absence creates the occasion for the encounter between Blodeuwedd and Gronw Pebyr, who arrives after hunting a stag by the river Cynvael. The palace’s court receives the tired hunter for the night, and the welcome opens the way to the affair and conspiracy that overturn Llew’s rule.

Seizure and Restoration

After Gronw strikes Llew with a poisoned dart, Gronw and Blodeuwedd go together to the palace. The following day Gronw takes possession of Ardudwy; after overcoming the land, he rules it, and both Ardudwy and Penllyn come under his sway. Mur y Castell thus stands at the heart of a political reversal: the home of a widely loved ruler becomes associated with the usurper who takes his territory in the aftermath of the attack.

The recovery of the palace begins when Gwydion, grieving for his nephew, searches for news of him. Once Llew has been healed and seeks retribution and the return of what is his, the whole of Gwynedd is summoned to march on Ardudwy. Gwydion goes ahead to Mur y Castell. Hearing of his approach, Blodeuwedd flees with her maidens toward a court on the mountain; their attempt to escape through the river Cynvael ends with the maidens drowning and Blodeuwedd being caught.

Narrative Significance

Mur y Castell anchors the movement from Llew’s legitimate, popular rule to Gronw’s occupation and the campaign to reclaim the land. Its location on the edge of Ardudwy matters to that sequence: the palace is not merely a dwelling, but the place from which rule over the surrounding territory is exercised and to which Gwydion’s force advances.

The contrast between the palace’s first description and its later role gives the setting its narrative weight. At first, it signifies a secure inheritance and a ruler accepted by his people; after Llew’s wounding, it becomes the site of a takeover, while Gwydion’s arrival marks the beginning of the reckoning that follows.