Tragédie en musique (Musical tragedy), also known as tragédie lyrique (French lyric tragedy), is a genre of French opera introduced by Jean-Baptiste Lully and used by his followers until the second half of the eighteenth century. Operas in this genre are usually based on stories from Classical mythology or the Italian romantic epics of Tasso and Ariosto. The stories may not have a tragic ending – in fact, they generally don't – but the atmosphere must be noble and elevated. The standard tragédie en musique has five acts. Earlier works in the genre were preceded by an allegorical prologue and, during the lifetime of Louis XIV, these generally celebrated the king's noble qualities and his prowess in war. Each of the five acts usually follows a basic pattern, opening with an aria in which one of the main characters expresses their feelings, followed by dialogue in recitative interspersed with short arias (petits airs), in which the main business of the plot occurs. Each act traditionally ends with a divertissement, offering great opportunities for the chorus and the ballet troupe. Composers sometimes changed the order of these features in an act for dramatic reasons.