In Aeschylus' Oresteia trilogy, Clytemnestra kills her husband, King Agamemnon because he had sacrificed their daughter Iphigenia to proceed forward with the Trojan war, and Cassandra, a prophetess of Apollo. Apollo gives an order through the Oracle at Delphi that Agamemnon's son, Orestes, is to kill Clytemnestra and Aegisthus, her lover. Orestes and Pylades carry out the revenge, and consequently Orestes is pursued by the Erinyes (Furies, female personifications of vengeance).
Apollo and the Furies argue about whether the matricide was justified; Apollo holds that the bond of marriage is sacred and Orestes was avenging his father, whereas the Erinyes say that the bond of blood between mother and son is more meaningful than the bond of marriage. They invade his temple, and he says that the matter should be brought before Athena. Apollo promises to protect Orestes, as Orestes has become Apollo's supplicant. Apollo advocates Orestes at the trial, and ultimately Athena rules in favor of Apollo.