The real-world counterpart of Bel-Aethne is the pagan celebration of Beltane, coming up on May 5th.
In the tradition of Moisehén, Bel-Aethne has its roots in the epic love of Aithne and Caradoc, the woman and man who first discovered magic. As a young girl, Eolyn learns their story, which forms the foundation of magical belief and thought in Moisehén:
. . .Aithne and Caradoc consecrated their love under a full spring moon, and the heat of their hearts sparked a fire in the center of the village. The villagers gathered in awe to observe the blaze. With branches of pine they divided the flame so that each family took a piece back to their own home. This is how fire came to our people. . .
Bel-Aethne, then, is a celebration of fire as well as of love and desire, all very powerful forms of Primitive Magic.
Dance and music play a central role in the high festival, which lasts for three days and culminates in the sacred rites of Aen-lasati, the awakening of the fire within. For one night the portals of magic are thrown open to all the people of Moisehén -- whether they are practitioners or not -- making all women Aithne and all men Caradoc, free to partake fully in the pleasure of the Gods and to experience the seeds of magic that transformed the history of their people.
The legend of Aithne and Caradoc is a transcendent myth in Eolyn's world. Pieces of it turn up throughout all three novels, in countless moments and countless ways. Even the mages of Tzeremond and Kedehen, who nearly destroyed the magas, could do little to diminish Aithne's importance in the imagination of their subjects. One of the climactic sequences of Eolyn takes place during an elaborate festival of Bel-Aethne, staged to celebrate the coronation of the new Mage King.
Here's a brief excerpt:
Even though Aithne and Caradoc were devoted lovers for the greater part of their lives, in Moisehén the liaisons created during the high festival of Bel-Aethne are considered ephemeral. According to an old saying of the Clan of East Selen, what is woven at Bel-Aethne becomes unraveled before the dawn.
This is not always true, of course, as Primitive Magic tends to break free of any rule we try to impose upon it. In fact, as part of the unrevealed backstory of Eolyn, one of the most enduring and troubled romances in the history of Moisehén -- that of Akmael's father Kedehen and his mother Briana of East Selen -- began with a kiss at Bel-Aethne.