All three Greek tragedians, Aeschylus, Sophocles and Euripides, have written plays related to Oresteia, a tragic tale of the seemingly relentless misfortunes of the House of Atreus, descendants of Tantalus. What distinguishes Aeschylus’ trilogy from the others, imo, is the use of the mystic character Cassandra and the depiction of the Eumenides, both are essential to the main theme of the trilogy, namely justice, from executing vengeance to trial by jury. The narrative is full of dark forebodings.
Cassandra
Cassandra was a priestess of Apollo and the daughter of King Priam of Troy who became a slave/concubine of Agamemnon after the fall of Troy. As a priestess with a gift of prophecy, Cassandra perceived the curses and misfortunes of the House of Atreus from a transcendent and historical perspective, how the sins of the fathers have been visited on their sons to many generations, from Tantalus to Agamemnon. She also foresaw the impending murder of Agamemnon and herself by his wife Clytaemestra and the murder of Clytaemestra by her own son Orestes. She questioned her unfortunate fate but accepted it bravely.
Eumenides
Eumenides, also known as the Furies, the goddesses of vengeance, represent the older generation of gods and the primitive conception of justice, whereas Athena and Apollo represent the younger generation and the new system of justice, i.e., trial by jury. Eumenides were despised, feared and shunned by both gods and men, because of their hideous office as prosecutor and executioner, and yet they did serve a necessary purpose in deterring crime, as Athena acknowledged in giving them a residence in her city Athens.
Influences
A few of Shakespeare’s plays might have been inspired by these characters: “Hamlet” (Orestes), “Macbeth” (Clytaemestra) and “The Merchant of Venice”, in which Shylock acts as the Furies and demands the “pound of flesh” and Portia as Athena ruling in favor of the accused. In Victor Hugo’s “Les Misérables”, Inspector Javert is another type of the Furies.
[Note: I don’t know why the publisher chose the painting “Achilles Receiving the Envoys of Agamemnon” as the cover image of Oresteia, since it has nothing to do with Achilles. He had enough troubles of his own without being entangled in others’ misfortunes.]