Leda and the Swan
by W. B. Yeats
 
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 5
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 10
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 — a figure in Greek mythology. The story varies slightly depending on the source, but Leda is raped by Zeus (king of the gods) on the same night she sleeps with her husband Tyndareus, the King of Sparta. As a result she produces two semi-divine children, a girl named Helen and a boy named Pollux (also known as Polydeuces), and two human children, a girl named Clytemnestra and a boy named Castor.

Helen grows up and marries Menelaus, who became King of Sparta, while Clytemnestra marries Agamemnon, King of Mycenae. Due to some further divine interference, Helen runs away with Paris, which leads to the Trojan War and ultimately, after ten years, the fall of Troy and the slaughter and enslavement of its inhabitants. Clytemnestra murders Agamemnon when he returns from the war, in some versions of the story because he had sacrificed their daughter Iphigenia to the gods.