What is the reference to the context of Agamemnon?

The structure of Agamemnon is marked by the tension between the stage action, the events of the past, and Agamemnon's anticipated return, which is the culmination of a series of increasingly exciting scenes in the first part of the play (1-781).

The prologue (1-39) is spoken by a watchman who has long been waiting for the beacon that is to signify the victory of the Greeks at Troy. Already there is an intimation that all is not well in his master's house (18f.). He paradoxically describes Clytemnestra as a woman with the heart and counsels of a man (11), and in his cryptic reference to circumstances in the palace (36-39) there is good reason to be apprehensive about Agamemnon's return.

The parodos is the longest continuous choral passage in extant Greek tragedy (40-257), a composition in which narrative and reflective sections are organically integrated. In this passage the chorus of old Argive men expounds, and tentatively interprets, the events that led to the Trojan War. The old men do not know, as the audience does, that the beacon has flashed, that the ten-year war is over, and that they can stop their anxious brooding at last.

The passage begins with the origins of the war. Zeus, one of whose functions (as Zeus Xenios) is to punish those who violate the law of hospitality, once sent the sons of Atreus, Agamemnon and Menelaus, against Troy because Paris, the Trojan prince, had abused Menelaus's hospitality by running off with his host's wife, Helen. But the launching of the expedition was attended by an ambiguous omen. The refrain—"Sing a dirge, a dirge, but may the good prevail!"—that the chorus weaves into its narrative applies not only to the omen but also to the course of the whole trilogy. Two eagles, the chorus relates, struck down a pregnant hare. According to the interpretation of the seer Calchas, whose words are reported by the chorus in direct speech, the omen is propitious: the Greeks will take Troy and all its treasures. But the sign also has its gloomy side: Artemis has been angered by the eagles' feast and, the seer reflects, could send adverse winds and delay the Greek ships. Everyone in the audience knows where the narrative is leading. Agamemnon will propitiate the goddess by sacrificing his daughter Iphigeneia.