Cornish mythology in the context of St Piran's Day

Avalon (/ˈævəlɒn/) is an island featured in the Arthurian legend. It first appeared in Geoffrey of Monmouth's 1136 Historia Regum Britanniae as a place of magic where King Arthur's sword Excalibur was made and later where Arthur was taken to recover from being gravely wounded at the Battle of Camlann. Since then, the island has become a symbol of Arthurian mythology, similar to Arthur's castle, Camelot.

Avalon was associated from an early date with mystical practices and magical figures such as King Arthur's sorceress sister Morgan, cast as the island's ruler by Geoffrey and many later authors. Certain Cornish and Welsh traditions have maintained that Arthur is an eternal king who had never truly died but would return as the "once and future" king. The particular motif of his rest in Morgan's care in Avalon has become especially popular. It can be found in various versions in many French and other medieval Arthurian and other works written in the wake of Geoffrey, some of them also linking Avalon with the legend of the Holy Grail.

Breton mythology is the mythology or corpus of explanatory and heroic tales originating in Brittany. The Bretons are the descendants of insular Britons who settled in Brittany from at least the third century. While the Britons were already Christianised in this era, the migrant population maintained an ancient Celtic mythos, similar to those of Wales and Cornwall.

Breton mythology has many gods and mythical creatures specifically associated with nature cults. In this tradition of gods and creatures rooted in nature, there exist traces of certain Breton Catholic saints.