Euripides, Iphigenia at Aulis 49–104: Prologue: Agamemnon explains the oath, the delay and Calchas' demand

Leda, the daughter of Thestius, had three children, maidens, Phoebe, Clytemnestra my wife, and Helen; the foremost of the favored sons of Hellas came to woo Helen; but terrible threats of spilling his rival’s blood were uttered by each of them, if he should fail to win the girl. Now the matter filled Tyndareus, her father, with perplexity, whether to give her or not, how he might best succeed. This thought occurred to him: the suitors should swear to each other and join right hands and pour libations with burnt-sacrifice, binding themselves by this curse: whoever wins the child of Tyndareus for wife, they will assist that man, in case a rival takes her from his house and goes his way, robbing her husband of his rights; and march against that man in armed array and raze his city to the ground, Hellene no less than barbarian. Now when they had once pledged their word and old Tyndareus with no small cleverness had beguiled them by his shrewd device, he allowed his daughter to choose from among her suitors the one towards whom the sweet breezes of Aphrodite might carry her. Her choice fell on Menelaus; would she had never taken him! Then there came to Lacedaemon from the Phrygians the man who, Argive legend says, judged the goddesses’ dispute; in robes of gorgeous hue, ablaze with gold, in true barbaric pomp; and he, finding Menelaus gone from home, carried Helen off, in mutual desire, to his steading on Ida. Goaded to frenzy, Menelaus flew through Hellas, invoking the ancient oath exacted by Tyndareus and declaring the duty of helping the injured husband.

And so the Hellenes, brandishing their spears and donning their harness, came here to the narrow straits of Aulis with armaments of ships and troops, with many horses and chariots, and they chose me to captain them all for the sake of Menelaus, since I was his brother. Would that some other had gained that distinction instead of me! But after the army was gathered and come together, we still remained at Aulis weatherbound. In our perplexity, we asked Calchas, the seer, and he answered that we should sacrifice my own child Iphigenia to Artemis, whose home is in this land, and we would sail and sack the Phrygians’ capital. When I heard this, I commanded Talthybius with loud proclamation to disband the whole army, as I could never bear to slay my daughter. Whereupon my brother, bringing every argument to bear, persuaded me at last to face the crime; so I wrote in a folded scroll and sent to my wife, bidding her despatch our daughter to me on the pretence of wedding Achilles, at the same time magnifying his exalted rank and saying that he refused to sail with the Achaeans, unless a bride of our lineage should go to Phthia. Yes, this was the inducement I offered my wife,