Zeus, Agamemnon, and the retention of authority

Pindar, Isthmian Ode 8 str3 - str5 : (5cBCE)

"When for marriage with Thetis there arose strife between Zeus and glorious Poseidon when each of the two gods would have her to be his lovely bride, for passion filled their hearts. But for them did the wisdom of the immortal gods not grant this union should come to pass, when to their ears came the prophetic oracle. For in their midst wise-counselled Themis told that it was ruled of fate that the sea-goddess should bring forth a son, of strength mightier than his father, whose hand should launch a shaft more powerful than the bolt of thunder or the fearsome trident, if she wed with Zeus or with his brothers. ‘Leave,’ said she, ‘From this design, but with a mortal let her bed be blessed, and let her see her son dying in war. Like Ares shall he be in strength of arm and in fleetness of foot like to the lightning flash. In my word you would hear, grant that her marriage be for an honour given of heaven to Peleus, the son of Aiakos, who, so they tell, is of all men most righteous, dwelling upon Iolkos' plain. And to the immortal cave of Kheiron (Chiron) let your bidding speedily take its way, nor let the ballot-leaves of strife be set amidst as twice by Nereus' daughter. But on the full-moon's eve let her for this hero unloose the lovely girdle of her pure maidenhood.’

Such words the goddess spoke to the children of Kronos; and they nodded giving their assent with immortal brows. Nor was the fruit of these words cast away. For the two gods joined in their honours given to the wedding of maid Thetis."

Sacrifice of Iphigenia

Hyginus Fabulae 98 (1cBCE)

When Agamemnon with his brother Menelaus and chosen leaders of Asia were going to Troy to recover Helen, wife of Menelaus, whom Alexander Paris had carried off, a storm kept them at Aulis because of the anger of Diana. Agamemnon had wounded a deer of hers in hunting, and had spoken rather haughtily against Diana. When he had called together the soothsayers, and Calchas had declared that he could expiate in no other way than by sacrificing his daughter, Iphigenia, Agamemnon at first refused. Then Ulysses by his advice won him over to a fine scheme. The same Ulysses along with Diomede was sent to get Iphigenia, and when he came to Clytemnestra her mother, he falsely said she was to be given in marriage to Achilles. When she was brought to Aulis, and her father was about to sacrifice her, Diana pitied the girl, cast mist about her, and substituted a deer in her place. She bore Iphigenia through the clouds to the Tauric land, and there made her a priestess of her temple.

Apollodorus, Epitome 3.21-22 (1-2 CCE)

But when they had put to sea from Argos and arrived for the second time at Aulis, the fleet was windbound, and Calchas said that they could not sail unless the fairest of Agamemnon's daughters were presented as a sacrifice to Artemis; for the goddess was angry with Agamemnon, both because, on shooting a deer, he had said, “Artemis herself could not (do it better),” and because Atreus had not sacrificed to her the golden lamb.

On receipt of this oracle, Agamemnon sent Ulysses and Talthybius to Clytaemnestra and asked for Iphigenia, alleging a promise of his to give her to Achilles to wife in reward for his military service. So Clytaemnestra sent her, and Agamemnon set her beside the altar, and was about to slaughter her, when Artemis carried her off to the Taurians and appointed her to be her priestess, substituting a deer for her at the altar; but some say that Artemis made her immortal.