Branwen, Daughter of Llyr is a major character in the Second Branch of the Mabinogi, which is sometimes called the Mabinogi of Branwen after her. Branwen is a daughter of Llyr and Penarddun and has been interpreted as the Welsh goddess of love and beauty. She is married to the King of Ireland, but the marriage does not bring peace.The story opens with Bendigeidfran (Bran the Blessed), King of Britain, sitting on a rock by the sea at Harlech and seeing the vessels of Matholwch King of Ireland approaching. Matholwch has come to ask for the hand of Bran's sister Branwen in marriage. Bran agrees to this, and a feast is held to celebrate the betrothal.
While the feast is going on, Efnisien, a half-brother of Branwen and Bran, arrived and asked why there were celebrations. On being told, he was furious that his half sister had been given in marriage without his consent, and vented his spleen by mutilating Matholwch's horses. Matholwch was deeply offended, but was conciliated by Bran who gave him a magical cauldron which could bring the dead to life.
Once in Ireland, Branwen was treated cruelly by her husband Matholwch as punishment for Efnisien's mutilation of the horses (though not before she gave birth to an heir, Gwern). She tamed a starling and sent it across the Irish Sea with a message to her brother and Bran brought an invasion force from Wales to Ireland to rescue her.
Some swineherds saw the giant Bran wading the sea and reported to Matholwch who retreated beyond a river and destroyed the bridges. However, Bran laid himself down over the river to serve as a bridge for his men. Matholwch, fearing war, tried to conciliate Bran and built a house big enough for him to fit into in order to do him honour. Matholwch agreed to give the kingdom to Gwern, his son by Branwen, to pacify Bran. The Irish lords didn't like the idea, so they hid themselves in flour bags tied to the pillars of the huge newly built house to attack the Welsh. Efnisien, checking out the house prior to the arrival of Bran and his men, guessed what was happening and killed the hidden men by squeezing their heads. At the subsequent feast to celebrate Gwern's investiture as King of Ireland, Efnisien threw his nephew Gwern into the fire in order to break the peace settlement. (Wikipedia)
