Llyr’s first wife was Iweriadd, or “Ireland,” the mother of the gigantic Bran the blessed, King of Britain and brother to Branwen, the goddess of love. According to others, it was Llyr’s wife Penarddun, the daughter of the mother goddess Don, who was Bran and Branwen’s mother.

According to the tale, King Matholwych of Ireland arrived in Harlech in Wales to marry Branwen. Efnisien, the strife bringer, angry at not having been consulted about the marriage, does harm to the Irish king’s horses, leading Bran to calm his angry brother-in-law by giving him a magic cauldron, the famous Cauldron of Plenty, which has the power to bring the wounded back to life.

In Ireland Branwen gives birth to Gwern, an heir who is to bring lasting peace between Bran and Matholwych, that is, between Wales and Ireland. But because of the evil deeds of Efnisien at the marriage in Wales, Branwen is harshly treated by her husband, being forced to work like a servant in the court kitchens and to bear the blows of the court butcher. Branwen teaches speech to a bird, however, and the bird flies off to Wales with a message to Bran describing his sister’s treatment. Furious, Bran invades Ireland, using his gigantic body to make a bridge between the lands so that his army can easily cross the sea. Matholwych agrees to peace, but Efnisien undermines the truce by throwing Gwern into a fire. In the battle that follows, Efnisien causes the destruction of the magic cauldron that had made possible the endless resuscitation of fallen Irish warriors. Bran is badly wounded, however, and instructs his followers to decapitate him and to take his head back to Britain. On the way home, Bran’s head continues talking and even eating. The war leaves Ireland with only five pregnant women alive to repopulate the island. Only a few Welsh, including Branwen and Taliesin, survive to return to Britain. Branwen dies of a broken heart over the war she blames herself for starting. Welsh deities, as did the Irish ones, could die.