 When Lully died in 1687 leaving his tragédie en musique "Achille et Polyxène" unfinished, Collasse completed the last four acts of the score.He went on to produce around a dozen operas and ballets, as well as sacred music, including settings of the "Cantiques spirituels" of Jean Racine.His plan to establish his own opera house in Lille ended in failure when the theatre burnt down.