Mythic, worshipped in ancient Greece, dates vary, beginning circa 1600 B.C.E.
Zeus, the ruler of Mount Olympus, seduced Leda, a mortal woman and the queen of Sparta, by transforming himself into a swan. According to one version of the myth, the offspring of this encounter—Clytemnestra and Helen of Troy—were hatched from a single egg. Clytemnestra ruled Mycenae with her husband, Agamemnon, who fought in the legendary Trojan War. While he was away, she had an affair with his enemy Aegisthus. When Agamemnon returned with a new wife, Cassandra, in tow, Clytemnestra murdered both of them. This story is told in the play Agamemnon by Aeschylus (525–456 B.C.E.).