Leda was the charming queen of Sparta, daughter of Testius. She had been the wife of Tyndaros king of Sparta, and by him she had had two daughters: Clytemnestra, who was later the wife of Agamemnon and Aegisthus, and Helen, for whose beauty the Trojan War occurred. Zeus fell in love with her and in order to see her he descended from the sky and reached the summit of Mount Taigeto. While Leda was sleeping on the banks of a pond, she was awakened by the squawking of the wings of a most candid swan; all around was the scent of ambrosia that stunned her, and the swan with its sinuous neck lovingly caressed her face, hair and arms. It was Zeus who, in order to approach her, transformed himself into a swan, and as soon as the young queen woke up, he made himself known to her and foretold her that from their love would be born twins, the Diòscuri: Càstore, a great horse tamer, and Pollúce, an invincible boxer. Both were to be the defense of the country and the guide of the sailors, who regarded the fire of St. Elmo as a sign of their protection. Since Càstore was mortal and Pollux immortal, the latter wanted to be mortal for love of his brother. Zeus, moved to pity, stipulated that each of them should live one day, alive, on Olympus and the next day, dead, in Erebo, thus taking turns .

Wonderful painting by Paolo Veronesi