The Oresteia is a trilogy of Greek tragedies written by Aeschylus which concerns the end of the curse on the House of Atreus. Though originally written as tetralogy, it is the only surviving example of a trilogy of ancient Greek plays; the fourth play, Proteus, a satyr play that would have been performed as finale, has not survived. The Oresteia was originally performed at the Dionysia festival in Athens in 458 BC, where it won first prize. Overall, this trilogy emblemizes the shift from a monarchal system of vendetta in Argos to a democratic system of litigation in Athens.

— Excerpted from Wikipedia, the free encyclopedia.