The story contains a mixture of the Greek myth of Orpheus with Celtic mythology and folklore concerning fairies, introduced into English via the Old French Breton lais of poets like Marie de France.
[3] The fragmentary Child Ballad 19, "King Orfeo", is closely related to this poem, the surviving text containing only portions of the known story.
Heurodis had visited the orchard the day before, accompanied by two maidens, to sleep beneath the shade of its branches; however, when she had awoken from her midday nap, she was so distressed that they had to call for the help of knights to restrain her.
Sir Orfeo wanders in the forest for many years, sleeping on the bare earth and living on berries and fruits in summer, roots and the bark of trees in winter.
He follows these ladies into a cliff and travels for three miles through the rock until he emerges into a fairy kingdom, a flat expanse of countryside presided over by a magnificent castle, built from gold and crystal and glass.
Quickly, the harp is recognized and Sir Orfeo explains that he found it ten years ago beside the mutilated body of a man who had been eaten by a lion.
[8] The poem shows Celtic influence in the Kingdom of the Fairies being a parallel dimension to the everyday world rather than the Land of the Dead as in the Greek myth of Orpheus and Eurydice.
Katharine Briggs sees the tale as related in British folk narratives as being equally influenced by Celtic stories such as The Wooing of Etain as it is from Classical sources, in particular the version of the story in Ovid’s Metamorphoses which would have been the most widely available source in Britain in the Middle Ages and for some time after[9] Thrace is identified at the beginning of the poem as "the old name for Winchester", which effectively announces that the well-known Greek myth is to be transposed into an English context: The poem's unique innovation, in comparison to the Orpheus and Eurydice myth, may be that the underworld is not a world of the dead, but rather a world of people who have been taken away when on the point of death.
Instead of having a Christian take on the myth, Vicari says, Sir Orfeo sticks to a rather pantheistic view, where the fairy king of Celtic literature rules over the underworld as neither good nor bad - as opposed to J. Friedman, who argues that Christian undertones relate Heurodis to Eve taken away by Satan in the form of a fairy king.
This Christian reading does not translate well overall, however: the Otherworld is described as attractive as well as menacing, and the fairy king is more a force of nature than an evil villain.
In the myth, Orpheus goes marching down to Tartarus to ask for Eurydice back while Sir Orfeo exiles himself for ten years until he chances a glimpse of his wife.
Orfeo obtains the Fairy King's permission to take his wife home with him by using his beautiful music playing, much the same as Orpheus did in the original Greek myth.
Sir Orfeo exiles himself for ten years, citing not wanting to see any more women after suffering the loss of his beautiful wife.
The loss of Eurydice, and the saving of Heurodis is the main difference between the tragedy of the original myth and the romance lai Sir Orfeo.
[15] This treatment of elements from Greek mythology is similar to that of the Old French literary cycle known as the Matter of Rome, which was made up of Greek and Roman mythology, together with episodes from the history of classical antiquity, focusing on military heroes like Alexander the Great and Julius Caesar – where the protagonists were anachronistically treated as knights of chivalry, not much different from the heroes of the chansons de geste.
"It lacks, however, any sense of chivalric values and ideals, and though the hero undergoes much suffering in the course of the story, this simply testifies to the power of his [Orfeo's] devotion and is not related to any scheme of self-realization.