Die Walküre
Wotan’s wife Fricka arrives in a chariot pulled by a ram.  Brünnhilde disappears, and there follows a big argument between husband and wife.  Fricka says to Wotan that Siegmund and Sieglinde must be punished for breaking Hunding's marriage, and for loving one another because brothers and sisters are not allowed to be lovers (this is called “incest”).  She says that she herself is the goddess of marriage and must make sure that marriage laws are obeyed. Fricka says that the gods will all be disgraced. Wotan says that he went to the world to have children with mortal women because the gods needed a race of heroes who would protect them.  But Fricka says to Wotan that he is wrong: Siegmund cannot be a free hero if he is being protected by Wotan. Giving in, Wotan now tells Brünnhilde that she must leave Siegmund to his fate.