The story from which the title is taken and on which the poem itself is based comes from an ancient Greek myth, in which Leda, wife to Tyndareus, King of Spartan, is raped or seduced by Zeus in the form of a swan. From this coupling, Leda gives birth to a total of four children, two from her husband and two from Zeus. The most famous of these children, later known as Helen of Troy, belonged to Zeus and it was her capture which triggered the Trojan War. After the war, the Romans would interpret and use this myth to trace their lineage and ancestry; this war is then considered one of the greatest events in Greek mythology, and is often seen as the inception of what we now know of as modern society.
Although the myth varies, typically Helen is said to be the daughter of Zeus and Leda. This is apt, since out of rape and violence was created beauty which instigated violence.