The House of Atreus Act I, released in 1999 is the first part of a metal opera inspired by the  only extant example of an ancient Greek theatre trilogy which won first prize at what festival?
Oresteia The Oresteia (Ancient Greek: Ὀρέστεια ) is a trilogy of Greek tragedies written by Aeschylus concerning the murder of Agamemnon by Clytaemnestra, the murder of Clytaemnestra by Orestes, the trial of Orestes, the end of the curse on the House of Atreus and pacification of the Erinyes. The trilogy—consisting of "Agamemnon" (Ἀγαμέμνων ), "The Libation Bearers" (Χοηφóρoι ), and "The Eumenides" (Εὐμενίδες )—also shows how the Greek gods interacted with the characters and influenced their decisions pertaining to events and disputes. The only extant example of an ancient Greek theatre trilogy, the "Oresteia" won first prize at the Dionysia festival in 458 BC. Many consider the "Oresteia" to be Aeschylus' finest work. The principal themes of the trilogy include the contrast between revenge and justice, as well as the transition from personal vendetta to organized litigation. "Orestia" originally included a satyr play, "Proteus" (Πρωτεύς ), following the tragic trilogy, but all except a single line of "Proteus" has been lost.
Idomeneo Idomeneo, re di Creta ossia Ilia e Idamante (Italian for "Idomeneus, King of Crete, or, Ilia and Idamante"; usually referred to simply as Idomeneo, K. 366) is an Italian language opera seria by Wolfgang Amadeus Mozart. The libretto was adapted by Giambattista Varesco from a French text by Antoine Danchet, which had been set to music by André Campra as "Idoménée" in 1712. Mozart and Varesco were commissioned in 1780 by Karl Theodor, Elector of Bavaria for a court carnival. He probably chose the subject, though it might have been Mozart. The work premiered on 29 January 1781 at the Cuvilliés Theatre in Munich, Germany.