La naissance d'Osiris, ou La fête Pamilie (The Birth of Osiris, or The Festival of Pamylia) is a one-act opera by Jean-Philippe Rameau, first performed on 12 October 1754 at Fontainebleau to celebrate the birth of the future King Louis XVI. The libretto is by Rameau's frequent collaborator Louis de Cahusac. Cahusac styled the work a ballet allégorique ("allegorical ballet"), but it is usually categorised as an acte de ballet. Its slender plot tells of Jupiter's announcement to a group of Egyptian shepherds of the birth of the god Osiris, who symbolises the baby prince. The piece may have started life as part of a larger work, Les beaux jours de l'Amour, an opéra-ballet Rameau and Cahusac planned but never completed for reasons which are still uncertain. Background and performance history Musicologists now think that Rameau and Cahusac originally intended La naissance d'Osiris to be part of a multi-act opéra-ballet called Les beaux jours de l'Amour. There is some evidence this work was substantially complete by May 1751, but for unknown reasons it was never staged. The other acts were Nélée et Myrthis (never completed and unperformed until the 20th century) and Anacréon, first performed separately at Fontainebleau on 23 October 1754. The Rameau scholar Sylvie Bouissou believes that La naissance would have been the first act of Les beaux jours de l'Amour. Like Anacréon, La naissance d'Osiris was salvaged for performance before the court at Fontainebleau. It thus became one of a series of operas celebrating the births of the children of the Dauphin of France and his wife Maria Josepha. On this occasion the royal baby was the Duc de Berry, the future King Louis XVI. The conductor Hugo Reyne notes the historical irony of identifying Louis XVI with Osiris, a god who was murdered, just as Louis was to be guillotined in 1793. The opera appeared on 12 October 1754 as part of a triple bill alongside revivals of Rameau's Pigmalion and Les incas de Pérou (the second act of the 1735 opéra-ballet Les Indes galantes). Documents show it went into rehearsal on 26 August, three days after the birth of the prince. The manuscripts show it was adapted for the occasion from Les beaux jours de l'Amour; originally Pamilie was merely an unnamed "shepherdess". A lengthy account of the premiere appeared in the October 1754 edition of the journal Le Mercure de France. In the same