Question:  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?
Context: The Persians (Ancient Greek: Πέρσαι , "Persai", Latinised as "Persae") is an ancient Greek tragedy written during the Classical period of Ancient Greece by the Greek tragedian Aeschylus.  It is the second and only surviving part of a now otherwise lost trilogy that won the first prize at the dramatic competitions in Athens’ City Dionysia festival in 472 BCE, with Pericles serving as "choregos". The Ichneutae (Ancient Greek: Ἰχνευταί , "Ichneutai", "trackers"), also known as the Searchers, Trackers or Tracking Satyrs, is a fragmentary satyr play by the fifth-century BC Athenian dramatist Sophocles.  Three nondescript quotations in ancient authors were all that was known of the play until 1912, when the extensive remains of a second-century CE papyrus roll of the "Ichneutae" were published among the Oxyrhynchus Papyri.  With more than four hundred lines surviving in their entirety or in part, the "Ichneutae" is now the best preserved ancient satyr play after Euripides' "Cyclops", the only fully extant example of the genre. Seven Against Thebes (Ancient Greek: Ἑπτὰ ἐπὶ Θήβας , "Hepta epi Thēbas"; ) is the third play in an Oedipus-themed trilogy produced by Aeschylus in 467 BC.  The trilogy is sometimes referred to as the Oedipodea.  It concerns the battle between an Argive army led by Polynices and the army of Thebes led by Eteocles and his supporters.  The trilogy won the first prize at the City Dionysia.  The trilogy's first two plays, "Laius" and "Oedipus", as well as the satyr play "Sphinx", are no longer extant. Aegisthus ( ; Ancient Greek: Αἴγισθος ; also transliterated as Aigisthos) is a figure in Greek mythology.  He was the son of Thyestes and his daughter, Pelopia.  The product of an incestuous union motivated by his father's rivalry with the house of Atreus for the throne of Mycenae, Aegisthus murdered Atreus to restore his father to power.  Later, he lost the throne to Atreus's son Agamemnon. Alcmaeon in Corinth (Ancient Greek: Ἀλκμαίων ὁ διὰ Κορίνθου , "Alkmaiōn ho dia Korinthou"; also known as "Alcmaeon at Corinth", "Alcmaeon") is a play by Greek dramatist Euripides.  It was first produced posthumously at the Dionysia in Athens, most likely in 405 BCE, in a trilogy with "The Bacchae" and "Iphigenia in Aulis".  The trilogy won first prize.  Except for a few fragments, "Alcmaeon in Corinth" has been lost.  Irish playwright Colin Teevan published a reconstruction of the play in 2005.  Approximately 23 fragments covering about 40 lines of "Alcmaeon in Corinth" are extant and were incorporated by Teevan in his reconstruction, although it is not certain that all these fragments belong to this play.  No complete scene has survived, nor has the cast of characters. The House of Atreus Act I, released in 1999, is the ninth studio album by the American heavy metal band Virgin Steele.  It has the subtitle "A Barbaric-Romantic Opera".  This album is the first part of a metal opera inspired by the Oresteia, a trilogy of Greek tragedies written by Aeschylus which concerns the end of the curse on the House of Atreus.  The music was intended to be the soundtrack for theatrical shows, with actors impersonating the characters of the tragedy.  The metal opera was actually performed under the name "Klytaimnestra - The House Of Atreus" in European theatres from 1999 to 2001, with the production of the Memmingen Opera House company and Landestheater Production. The Metal Opera: Pt 1 & 2 – Gold Edition is a box set by Avantasia, released through the band's former label AFM Records on March 6, 2008.  The set contains Avantasia's first two albums ("The Metal Opera" and "The Metal Opera Part II") on two gold CDs, a 44-page booklet with the storyline, rare photos, liner notes, and an interview with project mastermind Tobias Sammet; all inside a luxury leather box. The House of Atreus Act II, released in 2000, is the tenth studio album by the American heavy metal band Virgin Steele.  It was released as a double CD album.  This album is the second and final part of a metal opera inspired by the Oresteia, a trilogy of Greek tragedies written by Aeschylus which concerns the end of the curse on the House of Atreus.  The music was intended to be the soundtrack for theatrical shows, with actors impersonating the characters of the tragedy.  The metal opera was actually performed under the name "Klytaimnestra - The House Of Atreus" in European theatres from 1999 to 2001, with the production of the Memmingen Opera House company and Landestheater Production. 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. Edith Hall (born 1959) is a British scholar of classics, specialising in Ancient Greek Literature and cultural history, and Professor in the Department of Classics and Centre for Hellenic Studies at King's College London.  From 2006 until 2011 she held a Chair at Royal Holloway, University of London, where she founded and directed the Centre for the Reception of Greece and Rome until November 2011.  She resigned over a dispute regarding funding for classics after leading a public campaign, which was successful, to prevent cuts to or the closure of the Royal Holloway Classics department.  She also co-founded and is Consultant Director of the Archive of Performances of Greek and Roman Drama at Oxford University, Chairman of the Gilbert Murray Trust, and Judge on the "Stephen Spender Prize" for poetry translation.  Her prizewinning doctoral thesis was awarded at Oxford.  In 2012 she was awarded a Humboldt Research Prize to study ancient Greek theatre in the Black Sea, and in 2014 she was elected to the Academy of Europe.
Answer: the Dionysia festival