A sudden blow: the great wings beating still Above the staggering girl, her thighs caressed By the dark webs, her nape caught in his bill, He holds her helpless breast upon his breast. How can those terrified vague fingers push The feathered glory from her loosening thighs? And how can body, laid in that white rush, But feel the strange heart beating where it lies? A shudder in the loins engenders there The broken wall, the burning roof and tower And Agamemnon dead. Being so caught up, So mastered by the brute blood of the air, Did she put on his knowledge with his power Before the indifferent beak could let her drop?
Leda and the Swan eText - eText
The first two lines of this sonnet recount the Greek mythological account of Zeus, in the form of a swan, attacking and mating with Leda, a Spartan royal princess. The product of this rape is Helen, later the wife of Menelaus, King of Sparta.
The result of this rape is Helen, who later married King Menelaus of Sparta. She was then taken to Troy by Paris, a prince of Troy, and that act was the cause of the Trojan War, referred to by Yeats as "the broken wall, the burning roof and tower."
Yeats is emphasizing the fact that the act, for Zeus, was just another physical conquest of a beautiful woman, and Yeats wonders if Leda could have understood the implications of the rape.
Yeats implies that Leda, overcome with sexual emotion, gives in to Zeus's power.