Wikipedia
Dioclesian (The Prophetess: or, The History of Dioclesian) is a tragicomic semi-opera in five acts by Henry Purcell to a libretto by Thomas Betterton based on the play The Prophetess, by John Fletcher and Philip Massinger, which in turn was based very loosely on the life of the Emperor Diocletian. It was premiered in late May 1690 at the Queen's Theatre, Dorset Garden. The play was first produced in 1622. [??] Choreography for the various dances was provided by Josias Priest, who worked with Purcell on several other semi-operas.
Betterton reworked the play extensively, making room for a great deal of Purcell's music, notably in the 'monster' scene at the end of Act II and the final Masque about the victory of Love, which remained popular until well into the eighteenth century.
The premier production had a Prologue written by John Dryden that was suppressed after only one performance; it was far too critical of King William's military campaign in Ireland.