Efnisien, son of Euroswydd and Penarddun, emerges as a sinister figure within Welsh folklore, notably in the narrative of Branwen ferch Llŷr from the Mabinogi’s second branch. Often characterized as a sadistic anti-hero, with a psychopathic personality and a symbol of disruptive anti-social forces. He serves as the primary catalyst for the tragic events unfolding in the tale, ultimately leading to the ruin of both Ireland and the Island of the Mighty.

Bendigeid Vran, the son of Llyr, was the crowned king of this island, … And with him were his brother Manawyddan the son of Llyr, and his brothers by the mother’s side, Nissyen and Evnissyen, and many nobles likewise, as was fitting to see around a king. His two brothers by the mother’s side were the sons of Eurosswydd, by his mother, Penardun, the daughter of Beli son of Manogan.

The Second Branch of the Mabinogi: Branwen Daughter of Llyr

Efnisien’s lineage ties him closely to significant figures within Welsh mythology; he is the twin brother of Nisien and shares parentage with Brân the Blessed, Manawydan, and Branwen. Welsh Triads regard Llŷr as one of Britain’s Three Exalted Prisoners, highlighting his captivity under Euroswydd’s rule—a detail likely stemming from lost traditions surrounding the birth of Penarddun’s younger sons.

Efnisien in Welsh Celtic Literature

The tale unfolds as Matholwch, the Irish king, journeys to Harlech seeking an alliance with Brân the Blessed, the high king of the Island of the Mighty, by proposing marriage to Branwen, Brân’s sister. Brân grants Matholwch’s request, but festivities are marred when Efnysien, Brân’s half-brother, brutally mutilates Matholwch’s horses in a fit of rage for not being consulted about the marriage. To appease Matholwch’s offense, Brân offers a magical cauldron capable of reviving the dead. Content with the compensation, Matholwch and Branwen depart for Ireland.

In Ireland, Branwen gives birth to a son, Gwern, but Efnysien’s earlier transgression festers resentment among the Irish. Branwen endures mistreatment and is relegated to the kitchen, enduring daily beatings. Using a starling as her messenger, she implores Brân for rescue. Brân, accompanied by his brother Manawydan and a formidable army, sails to Ireland. The Irish attempt reconciliation, but Efnysien, sensing treachery, uncovers an ambush and slaughters the hidden warriors.

During a feast, Efnysien, feeling slighted once more, fatally burns Gwern, sparking a bloody conflict. Observing the Irish’s use of the cauldron to resurrect their fallen, Efnysien sacrifices himself by hiding among the dead and destroying the cauldron from within.

Amidst the carnage, only seven survivors remain, including Manawydan, Taliesin, and Pryderi, prince of Dyfed. Brân, mortally wounded, instructs them to take his severed head back to Britain. For seven years, they abide in Harlech, where Brân’s head continues to speak. They then dwell in Gwales for eighty years, oblivious to time’s passage until Heilyn fab Gwyn unwittingly reopens a door, prompting their sorrowful return.

Following Brân’s directive, they inter his silent head at Gwynfryn, the “White Hill,” believed to be where the Tower of London stands today, facing France to ward off invasion.