Yeats believed that history moved between different and contrary cycles. "Leda and the Swan" seems to be set at the exact turning point between two such cycles. Leda's world is populated by myths and divinities that come down to earth. But the world to which she gives "birth" is ruled by politics and power, not the gods. The Burning of Troy set the stage for the future rise of the Roman Empire and, much later, the rise of modern Europe.
- Title: The title of the poem alludes to an Ancient Greek myth and also to the many representations of this myth in Western art that share this title.
- Lines 10-11: These lines contain the poem's most direct allusion to Greek history. They describe the Burning of Troy and subsequent murder of Agamemnon, the most powerful Greek commander in the Trojan War. The poem claims that the birth of Helen of Troy, Leda's child by the swan, led to these events.
- Line 13: For most of the poem, the swan has been portrayed simply as a powerful bird. But here we learn that the swan has the "knowledge" of a god: Zeus.