In rode the Lord of the Nazgûl. A great black shape against the fires beyond he loomed up, grown to a vast menace of despair. In rode the Lord of the Nazgûl, under the archway that no enemy ever yet had passed, and all fled before his face.
All save one. There waiting, silent and still in the space before the Gate, sat Gandalf upon Shadowfax: Shadowfax who alone among the free horses of the earth endured the terror, unmoving, steadfast as a graven image in Rath Dínen.
"You cannot enter here," said Gandalf, and the huge shadow halted. "Go back to the abyss prepared for you! Go back! Fall into the nothingness that awaits you and your Master. Go!
The Black Rider flung back his hood, and behold! he had a kingly crown; and yet upon no head visible was it set. The red fires shone between it and the mantled shoulders vast and dark. From a mouth unseen there came a deadly laughter.
"Old fool!" he said. "Old fool! This is my hour. Do you not know Death when you see it? Die now and curse in vain!" And with that he lifted high his sword and flames ran down the blade.
And in that very moment, away behind in some courtyard of the city, a cock crowed. Shrill and clear he crowed, recking nothing of war nor of wizardry, welcoming only the morning that in the sky far above the shadows of death was coming with the dawn.
And as if in answer there came from far away another note. Horns, horns, horns, in dark Mindolluin's sides they dimly echoed. Great horns of the north wildly blowing. Rohan had come at last.

–J.R.R. Tolkien, The Lord of the Rings: The Re­turn of the King, "The Siege of Gon­dor" (Art by Angus McBride)