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 “Come not between the Nazgûl and his prey! Or he will not slay thee in thy turn. He will bear thee away to the houses of lamentation, beyond all darkness, where thy flesh shall be devoured, and thy shriveled mind be left naked to the Lidless Eye”

NAZGûL DESCRIPTION

THEIR APPEARANCE IN THE RING WORLD
“Immediately, though everything else remained as before, dim and dark, the shapes became terribly clear. He was able to see beneath their black trappings. There were five tall figures: two standing on the lip of the dell, three advancing. In their white faces burned keen and merciless eyes; under their mantles were long grey robes; upon their grey hairs were helms of silver; in their haggard hands were swords of steel.” – A Knife in the Dark, Fellowship of the Ring, p.208
THEIR APPEARANCE IN THE RING WORLD II
“He could see them clearly now; they appeared to have cast aside their hoods and black cloaks, and they were robed in white and grey. Swords were naked in their pale hands; helms were on their heads. Their cold eyes glittered, and they called to him with fell voices.” – Flight to the Ford, Fellowship of the Ring, p.226

NAZGûL HAVE FLESH, SINEWS
“No other blade, not though mightier hands had wielded it, would have dealt that foe a wound so bitter, cleaving the undead flesh, breaking the spell that knit his unseen sinews to his will.” – The Battle of Pelennor Fields, Return of the King, p.120

A “sinew” is a tendon, a band of tough, inelastic fibrous tissue that connects a muscle with its bony attachment.

NAZGûL CAN BE MISTAKEN AS MORTAL MEN
“It was in the beginning of the reign of Malvegil of Arthedain that evil came to Arnor. For at that time the realm of Angmar arose in the North beyond the Ettenmoors. Its lands lay on both sides of the Mountains, and there were gathered many evil men, and Orcs, and other fell creatures. [The lord of that land was known as the Witch-king, but it was not known until later that he was indeed the chief of the Ringwraiths, who came north with the purpose of destroying the Dúnedain in Arnor, seeking hope in their disunion, while Gondor was strong.]” – The North-kingdom and the Dúnedain, Appendix A, Return of the King, p. 320

THE WITCH-KING IN BATTLE
“Upon it sat a shape, black-mantled, huge and threatening. A crown of steel he bore, but between rim and robe naught was there to see, save only a deadly gleam of eyes: the Lord of the Nazgûl. To the air he had returned, summoning his steed ere the darkness failed, and now he was come again, bringing ruin, turning hope to despair, and victory to death. A great black mace he wielded.” – The Battle of Pelennor Fields, Return of the King, p.115

APPEARANCE OF THE NINE RINGS
“The Nine, the Seven and the Three each had their proper gem.” – Saruman as quoted by Gandalf, The Council of Elrond, Fellowship of the Ring, p.265

MINAS MORGUL AND THE NINE
“The valley of Minas Morgul passed into evil very long ago, and it was a menace and a dread while the banished Enemy dwelt yet far away, and Ithilien was still for the most part in our keeping. As you know, that city was one a strong place, proud and fair, Minas Ithil, the twin sister to our own city. But it was taken by fell men whom the Enemy in his first strength had been dominated, and who wandered homeless and masterless after his fall. It is said that their lords were men of Númenor who had fallen into dark wickedness; to them the Enemy had given rings of power, and he had devoured them: living ghosts they were become, terrible and evil. After his going they took Minas Ithil and dwelt there, and they filled it, and all the valley about, with decay: it seemed empty and it was not so, for a shapeless fear lived within the ruined walls. Nine Lords there were, and after the return of their Master, which they aided and prepared in secret, they grew strong again. Then the Nine Riders issued forth from the gates of horror, and we could not withstand them. Do not approach their citadel. You will be espied. It is a place of sleepless malice, full of lidless eyes. Do not go that way!” – Faramir, The Forbidden Pool, The Two Towers, p.301