Branwen, the daughter of Llŷr, is a main character in a medieval Welsh story called the Second Branch of the Mabinogi. This story is sometimes named the "Mabinogi of Branwen" because it focuses on her. Branwen is the daughter of Llŷr and Penarddun. She marries Matholwch, the king of Ireland. However, their marriage does not lead to peace.

Her story

The story begins with Branwen’s brother, Brân the Blessed, a giant and king of Britain, sitting on a rock by the sea at Harlech. He sees the ships of Matholwch, king of Ireland, approaching. Matholwch has come to ask for Branwen’s hand in marriage. Brân agrees, and a feast is held to celebrate their engagement. During the feast, Efnysien, a half-brother of Branwen and Brân, arrives at the stables and asks about the celebration. When told the reason, he becomes angry because his half-sister was given in marriage without his approval. In a rage, he damages the horses belonging to the Irish. Matholwch is very upset but is calmed by Brân, who gives him a magical cauldron that can bring the dead back to life. Brân does not know that the resurrected people will be unable to speak or hear.

When Matholwch returns to Ireland with his new bride, he talks to his nobles about the events in the Isle of the Mighty. They are angry and believe Matholwch was not treated fairly for the harm done to his horses. To restore his honor, Matholwch sends Branwen to work in the kitchens as punishment. Branwen is treated poorly by Matholwch, though she first gives birth to their son, Gwern. She tames a starling and sends it across the Irish Sea with a message to her brother. Brân gathers an army from Wales to rescue her.

Some swineherds see the giant Brân walking through the sea and tell Matholwch, who retreats beyond a river and destroys the bridges. Brân lies across the river to act as a bridge for his men, saying, “He would be a leader, let him be a bridge.”

Matholwch, fearing war, tries to make peace with Brân by building a house large enough for him to fit inside as a sign of respect. He agrees to give the kingdom to Gwern, his son with Branwen, to please Brân. The Irish lords dislike this plan and hide in flour bags tied to the pillars of the new house to attack the Welsh.

Efnysien, checking the house before Brân and his men arrive, finds the hidden men and kills them all by crushing their heads one by one. At a later feast celebrating Gwern’s coronation as king of Ireland, Efnysien suddenly throws his nephew Gwern into a fire. This causes war between the two countries. The Irish forces at first lose, but they win by using the magical cauldron to bring their dead soldiers back to life. Efnysien realizes his mistake and, pretending to be a dead Irish soldier, is thrown into the cauldron. He pushes against its walls until it breaks into four pieces. Efnysien dies in the attempt. The war is very deadly, and only Branwen, Brân, and seven Welsh soldiers survive. They sail back to Wales.

When they arrive in Wales, they learn that Brân has been wounded by a poisoned arrow in his leg and dies. Branwen, heartbroken by all the losses, dies from grief.

War against Ireland

After the war, all the Irish are killed except for five pregnant women from Wales who help repopulate the island. Only seven Welsh people survive and return to Wales with Branwen, carrying the severed head of Bendigeidfran. When they arrive at Aber Alaw in Anglesey, Branwen dies from sorrow, saying, "Oh Son of God, my life is a curse! Two beautiful islands were destroyed because of me!" She is buried near the Afon Alaw.

Before his death, Brân ordered his men to cut off his head and carry it to the White Mount in London, where it should be buried with the face facing France. For seven years, his men feasted in Harlech, accompanied by three singing birds and Brân's head. Later, they traveled to Gwales in Penfro, where they stayed for eighty years. Eventually, they went to London and buried Brân's head at the White Mount. A legend claimed that as long as the head remained there, no enemy forces would attack Britain by sea.

Branwen's Grave

At Llanddeusant, Anglesey, near the Alaw River, there is a cairn called Bedd Branwen, which is believed to be her grave. The site is now in ruins but still has one standing stone. In 1800, the area was dug up. Later, in the 1960s, Frances Lynch excavated the site and found several urns containing human ashes. Some believe that if the story of Branwen is based on real events, those events likely happened during a time in the Bronze Age history of Britain.