The arthurian legend is especially known for the version wrote by Geoffroy de Monmouth, in the 12th century, based on ancient stories in Welsh. It originated from Great Britain, in Wales, and developed across the Channel, in Armorica (the “small Brittany”).

It should be said that in Brittany, beyond the myth, the name of Arthur had a political significance starting from the 12th century, giving to a prince an unrivalled aura and legitimacy vis-a-vis the English and French claims or dominations: thus Constance, grand-daughter of Henri II Plantagenêt, was the first to name her son Arthur, against the opinion of the powerful dynasty; this name was rare at that time, but it testifies to the increasing popularity of the Arthurian myth among the Plantagenêts. In the end, three dukes of Brittany would be named Arthur, until the 15th century.

The mythical forest of Brocéliande is the setting of the legends, the stories and appearances of the characters of the Arthurian cycle and the Knights of the Round Table: king Arthur and queen Guenièvre, the knight Lancelot, the wise man Merlin, the fairy Viviane,…

But Arthur is also present in the Trégor, where we can discover testimonys of his legendary visit. This mythical hero of the literature and of the medieval oral tradition could have been based on historical facts: a hero of this name would have lived in Great Britain in the end of the 5th century - in the beginning of the 6th century, and would have fought the Saxon invader.

In Saint-Efflam:
The Britons from across the English Channel carried with them the legendary life of King Arthur. The most famous scene in the Trégor is that of Arthur, on the Lieue-de-Grève, between Saint-Michel and Plestin, fighting a dragon. Arthur, exhausted, was helped by one of the 800 saints who came to evangelize Armorica, Saint Efflam. He created a source making water spouting out from the ground so that Arthur could slake his thirst: the tradition said that the source is located in Saint-Efflam. At the end of the 16th century, the source was covered with an imposing building, where the statues of Saint Efflam and Saint Enora, his wife, now disappeared, were housed.

In Perros-Guirec:
After a short prayer from Saint Efflam, the dragon drowned in the ocean, blood gushing from its mouth, nostrils and eyes. The popular tradition says that this scene is represented on an outside foot of the Romanesque church of Saint-Jacques.

In Pleumeur-Bodou, in the castle of Kerduel:
Built between the 13th and the 14th century, the castle of Pleumeur-Bodou houses a “room of King Arthur.” Kerduel phonetically resembles Caerduel, one of Arthur’s residences, according to the tradition. Legend has it that on certain nights Arthur walks the paths of the castle on his white horse.

In Pleumeur-Bodou again, on the island of Aval:
Near the Île-Grande, King Arthur is said to be dormant, healing his wounds, before reuniting his people on both sides of the Channel and returning to his throne.

The island of Aval or Enez aval, now privately owned, is one of the most famous small islands on the Breton coast. According to the legend, King Arthur is buried there, and the Bretons on both sides of the Channel await his awakening which will restore the Celtic unity. Around the 6th century, monks are said to have built a monastery there. In the centre of the island stood a chapel dedicated to Saint Marc. In the middle of the old monastic cemetery, stand a menhir and a Merovingian cross. It was Félix Le Dantec’s father who, in 1878, reported to the Anthropological Society of Paris the presence of skeletons with elongated heads, which prove that the island was inhabited during the early Middle Ages. The bones were transported to the Ile-Grande cemetery.

Pleumeur-Bodou is thus one of the most famous Arthurian site of Brittany, after Broceliande.

Sources:
Blog Ile-Grande.bzh: Ile d’Aval
Wikipedia: Pleumeur-Bodou, beliefs and legends
Wikipedia: Arthur I duke of Brittany