In rode the Lord of the Nazgul. A great black shape against the fires beyond, he loomed up, grown to a vast menace of despair. In rode the Lord of the Nazgul, under the arch 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 Shadofax, Shadowfax who alone among the free horses of the earth endured the terror, unmoving, steadfast as a graven image in Rath Dinen. The Lord of the Rings Page 861