From Eaters of the Dead:
I inquired why the black mist had returned, and he lowered his voice to speak this reply: "The black mist has come from the vanity and weakness of Rothgar, who has offended the gods with his foolish splendor and tempted the fiends with the sitting of his great hall, which has no protection from the land. Rothgar is old and he knows he will not be remembered for battles fought and won, and so he built this splendid hall, which is the talk of all the world, and pleases his vanity. Rothgar acts as a god, yet he is a man, and the gods have sent the black mist to strike him down and show him humility."