Just about everything you wanted to know about the Nazgûl but were too lazy to look it up for yourself.

This is by no means an exhaustive listing of quotes about Nazgûl, but it is fairly complete with quotes taken from Fellowship of the Ring,
The Two Towers, Return of the King, The Silmarillion, Unfinished Tales, Tolkien Letters, and the History of Middle-earth series.

Quotes provided by The Library of Minas Morgul.

"SINISTER CAVALIERS"
In 1969, J. R. R. Tolkien collaborated with artist Pauline Baynes to create a map of Middle-earth. Baynes' map can easily be found through image searches, although one should keep in mind that there are two versions of the map circulating the internet. The original version of the map has a drawing of the Fellowship of the Ring on the top, and a drawing of orcs, Gollum, the Nazgûl, and Shelob on the bottom. However, a cropped version of the map also exists. The following two quotes refer to the full version of the image.

Other comments are less positive: e. g. of the vignettes he [Tolkien] signaled out those of Minas Tirith and Hobbiton for particular dislike; and of the depictions of characters he most disliked those of Gandalf, Legolas, Gollum, the Black Riders (though he found them "impressive as sinister cavaliers", he decried the addition of "hats and plumes" and the "relief" of their hell-black with elvish green" [...]
--"Character Descriptions," The Nature of Middle-earth, edited by Carl F. Hostetter, p. 190.

THE NAZGûL WERE NOT SKELETAL
They are clearly described as being themselves invisible and clad in long black cloaks with great hoods that hung down over their faces, so that people they met would not realize that they had no visible faces (I 84). Neither could their hands be seen. In any case horsemen so accoutered would have worn gauntlets. Nor of course would their limbs have been so thin and emaciated if visible. (I 84 refers to the scene in Fellowship of the Ring where Frodo encounters Khamûl in the Shire)
--"Character Descriptions," The Nature of Middle-earth, edited by Carl F. Hostetter, p. 196.

THREE OF THE NAZGUL WERE NUMENOREAN
Yet Sauron was ever guileful, and it is said that among those whom he ensnared with the Nine Rings three were great lords of Númenórean race.
--"Akallabêth," The Silmarillion, p. 267.

MOST LIKELY THE NUMENOREAN NAZGÛL HAD NO BEARDS
None of the Eldar had any beards, and this was a general racial characteristic of all Elves in my "world." Any element of an Elvish strain in human ancestry was very dominant and lasting (receding only slowly - as might be seen in Númenóreans of royal descent, in the matter of longevity also). […] But the royal house was half-elven, having two strains of Elvish race in their ancestry through Luthien of Doriath (royal Sindarin) and Idril of Gondolin (royal Noldorin) The effects were long-lasting: e. g. in a tendency to a stature a little above the average, to a greater (though steadily decreasing) longevity, and probably most lastingly in beardlessness. Thus none of the Númenóreans chieftains of descent from Elros (whether kings or not) would be bearded.
--"Beards," The Nature of Middle-earth, edited by Carl F. Hostetter, p. 187-88.

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

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

NAZGUL SENSE THE PRESENCE OF OTHER NAZGUL
"The Nazgûl found one another easily, since they were quickly aware of a companion presence, and could hear the cries over great distances. They could see one another also from far away, even by day, when to them a Nazgûl was the one clearly visible thing in a mist." ­ Marquette MSS 4/2/36 (The Hunt for the Ring), Reader's Companion by Hammond and Scull, p. 164

THE ASHES OF GORGOROTH STIRRED...
"And in the days of Telemnar, the third and twentieth of the line of Meneldil, a plague came upon dark winds out of the east, and it smote the King and his children, and many of the people of Gondor perished. Then the forts on the borders of Mordor were deserted, and Minas Ithil was emptied of its people; and evil entered again into the Black Land secretly, and the ashes of Gorgoroth were stirred as by a cold wind, for dark shapes gathered there. It is said that these were indeed the Úlairi, whom Sauron called the Nazgûl, the Nine Ringwraiths that had long remained hidden, but returned now to prepare the ways of their Master, for he had begun to grow again.
"And in the days of Eärnil they made their first stroke, and they came by night out of Mordor over the passes of the Mountains of Shadow, and took Minas Ithil for their abode; and they made it a place of such dread that none dared to look upon it. Thereafter it was called Minas Morgul, the Tower of Sorcery; and Minas Morgul was ever at war with Minas Anor in the west. Then Osgiliath, which in the waning of the people had long been deserted, became a place of ruins and a city of ghosts." - "Of the Rings of Power and the Third Age," The Silmarillion, p.298-297

NOT DEATH, BUT FADING
"A mortal, Frodo, who keeps one of the Great Rings, does not die, but he does not grow or obtain more life, he merely continues, until at last every minute is a weariness. And if he often uses the Ring to make himself invisible, he fades: he becomes in the end invisible permanently, and walks in the twilight under the eye of the dark power that rules the Rings. Yes, sooner or later - later, if he is strong or well-meaning to begin with, but neither strength nor good purpose will last - sooner or later, the dark power will devour him." - Gandalf, "The Shadow of the Past," Fellowship of the Ring, p.56

ALL FELL TO THE POWER OF THEIR RINGS
"Those who used the Nine Rings became mighty in their day, kings, sorcerers, and warriors of old. They obtained glory and great wealth, yet it turned to their undoing. They had, as it seemed, unending life, yet life became unendurable to them. They could walk, if they would, unseen by all eyes in this world beneath the sun, and they could see things in worlds invisible to mortal men; but too often they beheld only the phantoms and delusions of Sauron. And one by one, sooner or later, according to their native strength and to the good or evil of their wills in the beginning, they fell under the thralldom of the ring that they bore and of the domination of the One which was Sauron's. And they became forever invisible save to him that wore the Ruling Ring, and they entered into the realm of shadows. The Nazgûl were they, the Ringwraiths, the Enemy's most terrible servants; darkness went with them, and they cried with the voices of death." - Of the Rings of Power and the Third Age, The Silmarillion, p.289

CANNOT ACT AGAINST SAURON'S WILL
"They were by far the most powerful of his servants, and the most suitable for such a mission, since they were entirely enslaved to their Nine Rings, which he now himself held; they were quite incapable of acting against his will, and if one of them, even the Witch-king their captain, had seized the One Ring, he would have brought it back to his Master." - Unfinished Tales

FOLK OF MORDOR FEAR THEM
"But it is the Black Captain who defeats us. Few will stand and abide even the rumor of his coming. His own folk quail at him, and they would slay themselves at his bidding." - Siege of Gondor, Return of the King, p.91

OF KHAMûL
"Of Khamûl it is said here that he was the most ready of all the Nazgûl, after the Black Captain himself, to perceive the presence of the Ring, but also the one whose power was the most confused and diminished by daylight." - Unfinished Tales, The Hunt for the Ring

HAVE MINDS AND WILLS (BUT ARE NOT INFALLIBLE)
"Now silently the host of Rohan moved forward into the field of Gondor, pouring in slowly but steadily, like the rising tide through breaches in the dike that men had thought secure. But the mind and will of the Black Captain were bent wholly on the falling city, and as yet no tidings came to him warning him that his designs held any flaw." - Siege of Gondor, Return of the King, p.111

INTELLIGENT BEINGS; NOT ROBOTS
"But it was no orc-chieftain or brigand that led the assault upon Gondor. The darkness was breaking too soon, before the date that his Master had set for it: fortune had betrayed him for the moment, and the world had turned against him; victory was slipping from his grasp even as he stretched out his hand to seize it. But his arm was long. He was still in command, wielding great powers. King, Ringwraith, Lord of the Nazgûl, he had many weapons. He left the gate and vanished." - Battle of the Pelennor Fields, Return of the King, p.114

NOT BY THE HAND OF MAN...
"But it is said when all was lost suddenly the Witch-king himself appeared, black-robed and black-masked upon a black horse. Fear fell upon all who beheld him; but he singled out the Captain of Gondor for the fullness of his hatred, and with a terrible cry he rode straight upon him. Eärnur would have withstood him; but his horse could not endure that onset, and it swerved and bore him far away before he could master it.
"Then the Witch-king laughed, and none that heard it ever forgot the horror of that cry. But Glorfindel rode up then on his white horse, and in the midst of his laughter the Witch-king turned to fight and passed into the shadows. For night came down on the battlefield, and he was lost, and none saw whether he went.
"Eärnur now rode back, but Glorfindel, looking into the gathering dark, said: 'Do not pursue him! He will not return to this land. Far off yet is his doom, and not by the hand of man will he fall.' -Appendix A, Return of the King, p.331

WITCH-KING REDUCED TO IMPOTENCY; RING A POWERFUL SYMBOL IN RELIGIOUS CULT
"The situation as between Frodo with the Ring and the Eight [Footnote: The Witch-king had been reduced to impotence] might be compared to that of a small brave man armed with a devastating weapon, faced by eight savage warriors of great strength and agility armed with poisoned blades. The man's weakness was that he did not know how to use his weapon yet; and he was by temperament and training adverse to violence. Their weakness that the man's weapon was a thing that filled them with fear as an object of terror in their religious cult, by which they had been conditioned to treat one who wielded it with servility." - Letter #246, Tolkien Letters, p. 331

THE FATE OF EäRNUR
"Eärnur had held the crown only seven years when the Lord of Morgul repeated his challenge, taunting the king that to the faint heart of his youth he had now added the weakness of age. Then Mardil could no longer restrain him, and he rode with a small escort of knights to the gate of Minas Morgul. None of that riding were ever heard of again. It was believed in Gondor that the faithless enemy had trapped the king, and that he had died in torment in Minas Morgul; but since there were no witnesses of his death, Mardil the Good Steward ruled Gondor in his name for many years." -Appendix A, Return of the King, p.331

AFTER FRODO CLAIMED THE RING
"Sauron sent at once the Ringwraiths. They were naturally fully instructed, and in no way deceived as to the real lordship of the Ring...But the situation was now different to that under Weathertop, where Frodo acted merely in fear and wished only to use (in vain) the Ring's subsidiary power of conferring invisibility. He had grown since then. Would they have been immune from its power if he claimed it as an instrument of command and domination? Not wholly. I do not think they could have attacked him with violence, nor laid hold upon him or taken him captive; they would have obeyed or feigned to obey any minor command of his that did not interfere with their errand - laid upon them by Sauron, who still through their nine rings (which he held) had primary control of their wills..." Letter 246, Tolkien Letters

THE WITCH-KING'S MISTAKES AT WEATHERTOP; FEAR OF FRODO, ARAGORN AND GANDALF; AND ASSUMPTIONS THAT FRODO IS IN LEAGUE WITH THE ELVES
"The camp is attacked at night by [five Riders]; but they are driven off by Aragorn; and withdraw after wounding Frodo. [The Witch-king] now knows who is the Bearer, and is greatly puzzled that it should be a small creature, and not Aragorn, who seems to be a great power though apparently [only a Ranger'. But the Bearer has been marked with the Knife and (he thinks) cannot last more than a day or two.
"It is a strange thing that the camp was not watched while darkness lasted of the night Oct. 6-7, and the crossing of the road into the southward lands seems not to have been observed, so that [the Witch-king] again lost track of the Ring. For this there were probably several reasons, the least to be expected being the most important, namely that [the Witch-king], the great captain, was actually dismayed. He had been shaken by the fire of Gandalf, and began to perceive that the mission on which Sauron had sent him was one of great peril to himself both by the way, and on his return to his Master (if unsuccessful); and he had been doing ill, so far achieving nothing save rousing the power of the Wise and directing them to the Ring. but above all the timid and terrified Bearer had resisted him, had dared to strike at him with an enchanted sword made by his own enemies long ago for his destruction. Narrowly it had missed him. How he had come by it - save in the Barrows of Cardolan. Then he was in some way mightier than the B[arrow]-wight; and he called on Elbereth, a name of terror to the Nazgul. He was then in league with the High Elves of the Havens.
"Escaping a wound that would have been as deadly to him as was the Mordor-knife to Frodo (as was proved at the end), he withdrew and hid for a while, out of doubt and fear both of Aragorn and especially of Frodo. But fear of Sauron, and the forces of Sauron's will was the stronger.
"Oct. 7. He arose and cried out to his companions, and drew [the other four] back to him. He then patrols the Road to the Bridge of Mitheithel, knowing that it was practically impossible to cross the Greyflood between Tharbad and the Bridge (while [the four Riders who pursued Gandalf] are away north along the upper river). The Nazgul search in vain for the Bearer while Aragorn leads Frodo in the pathless lands south of the Road."
--J. R. R. Tolkien, quoted in Marquette MSS 4/2/36, The Lord of the Rings A Readers Companion, Wayne G. Hammond and Christina Scull, p. 180-1

THE WITCH-KING CHOOSES NOT TO CHALLENGE GLORFINDEL; HE AND KHAMUL "WASTE TIME" WHILE HUNTING FOR FRODO
"Oct. 11: Glorfindel reaches Bridge of Mitheithel and there finds [three Riders, including Khamul]. He drives them back well down the road, until they leave it and disperse. (Thus Aragorn and Frodo cross safely on Oct. 13). Glorfindel meets [the Witch-king and another Rider] coming east along road, but [the Witch-king] cannot challenge him (esp[ecially] by day) with so small help; he flees into the pathless lands.
"Oct. 14. [These five Riders] reassemble and start in pursuit again. [The Witch-king and Khamul] perceive that Ring crossed Bridge but lose trail, and waste time hunting about.
"Oct. 19: They become aware of the Ring not far ahead."
--J. R. R. Tolkien, quoted in Marquette MSS 4/2/36, The Lord of the Rings A Readers Companion, Wayne G. Hammond and Christina Scull, p. 194

NAZGUL "TIMID" WITHOUT THEIR KING
"Several of the Nazgul must remain in A[nduin] Vale. One or more actually direct the attack on Thranduil when Gollum escapes. Sauron thinks it vital to have him captured again and/or killed. 2/3 Nazgul still prowl about Rohan and [?] in Dunland, and up towards Eregion. They are rather timid and ineffectual without [the] W[itch]-king. Also they will not cross Greyflood into 'enemy Elvish country' without his leadership or express command. The ?major force of N[azgul] 5/6 are engaged in hunt in Anduin Vale and forest etc. for Gollum..."
--J. R. R. Tolkien, quoted in Marquette MSS 4/2/35, The Lord of the Rings A Readers Companion, Wayne G. Hammond and Christina Scull, p. 242-3. In this note, Tolkien was trying to solve chronological problems that occured when writing "The Hunt for the Ring," the account of the Nazgul's search for the Ring in Unfinished Tales.

THEIR POWER WOULD INCREASE IF SAURON REGAINED THE RING
“The Ringwraiths are deadly enemies, but they are only shadows yet of the power and terror they would possess if the Ruling Ring was on their master’s hand again.”
-- Gandalf, “A Journey in the Dark,” Fellowship of the Ring, 331

DAYLIGHT AND WATER AS WEAKNESSES; STRENGTH IN NUMBERS
All except the Witch-king were apt to stray when alone by daylight; and all, again save the Witch-king, feared water, and were unwilling, except in dire need, to enter it or to cross streams unless dryshod by a bridge. Moreover their chief weapon was terror. This was actually greater when they were unclad and invisible; and it was greater also when they were gathered together.
--"The Hunt for the Ring: Other Versions of the Story," Unfinished Tales

NONE COULD WITHSTAND THEIR TERROR WHEN THEY WERE GATHERED TOGETHER
Now few could understand even one of these fell creatures, and (as Sauron deemed) none could withstand them when gathered together under their terrible captain, the Lord of Morgul. Yet this weakness they had for Sauron's present purpose: so great was the terror that went with them (even invisible and unclad) that their coming forth might soon be perceived and their mission be guessed by the Wise.
--"The Hunt for the Ring: Other Versions of the Story," Unfinished Tales

THE WITCH-KING CAN BLOW UP SWORDS
"Then the leader, who was now half across the Ford, stood up menacing in his stirrups, and raised up his hand. Frodo was stricken dumb. He felt his tongue cleave to his mouth, and his heart labouring. His sword broke and fell out of his shaking hand. The elf-horse reared and snorted. The foremost of the black horses had almost set foot upon the shore." - Flight to the Ford, Fellowship of the Ring, p.227

MAKE SWORDS FLAME
"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 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." - The Siege of Gondor, Return of the King, p.103

SNOW AND ICE
"Lossoth, the Snow Men of Forchel ... they were afraid of the Witch-king, who (they said) could make frost or thaw at his will." - Appendix A, The North Kingdom and the Dúnedain, Return of the King, p.322

SNOW AND ICE II
"But the snow men were uneasy; for they said they smelled danger in the wind. And the chief of the Lossoth said to Arvedui: 'Do not mount on this sea-monster! If they have them, let the seamen bring us food and other things that we need, and you may stay here till the Witch-king goes home. For in summer his power wanes; but now his breath is deadly, and his cold arm is long.'" - Appendix A, The North Kingdom and the Dúnedain, Return of the King, p.322

CAN USE SORCERY TO DESTROY THINGS
"The drums rolled and rattled. With a vast rush Grond was hurled forward by huge hands. It reached the Gate. It swung. A deep boom rumbled through the city like thunder running in the clouds. But the doors of iron and posts of steel withstood the stroke.
"Then the Black Captain rose in his stirrups and cried aloud in a dreadful voice, speaking in some forgotten tongue words of power and terror to rend both heart and stone.
"Thrice he cried. Thrice the great ram boomed. And suddenly upon the last stroke the Gate of Gondor broke. As if stricken by some blasting spell, it burst asunder: there was a flash of searing lightning, and the doors tumbled in riven fragments to the ground." - Siege of Gondor, Return of the King, p.102

PRIMARY WEAPON FEAR
[Nazgûl] "Their peril is almost entirely due to the unreasoning fear which they inspire (like ghosts). They have no great physical power against the fearless; but what they have, and the fear that they inspire, is enormously increased in darkness. The Witch-king, their leader, is more powerful in all ways than the others; but he must not yet be raised to the stature of Vol. III. There, put in command by Sauron, he is given an added demonic force. But even in the Battle of the Pelennor, the darkness had only just broken. See III 114." - Letter 210, Tolkien Letters, p.272

IN DARKNESS AND LONELINESS
"In dark and loneliness they are strongest; they will not openly attack a house where there are lights and many people - not until they are desperate, not while all the long leagues of Eriador still lie before us. But their power is in terror, and already some in Bree are in their clutch. They will drive these wretches to some evil work: Ferny, and some of the strangers, and, maybe, the gatekeeper too. They had words with Harry at Westgate on Monday. I was watching them. He was white and shaking when they left him." - Aragorn, Strider, Fellowship of the Ring, p. 186

THE BLACK BREATH
"But now their art and knowledge were baffled; for there were many sick of a malady that would not be healed; and they called it the Black Shadow, for it came from the Nazgûl. And those who were stricken with it fell slowly into an ever deeper dream, and then passed to silence and a deadly cold, and so died." - Houses of Healing, Return of the King, p.136

BLACK SHADOW IN BREE & DEALINGS WITH FERNY
"[Merry] gasped: 'I have seen them, Frodo! I have seen them! Black Riders! ... Here. In the village. I stayed indoors for an hour. Then as you did not come back, I went out for a stroll. I had come back again and was standing just outside the light of the lamp looking at the stars. Suddenly I shivered and felt that something horrible was creeping near: there was sort of a deeper shade among the shadows across the road, just beyond the edge of lamplight. It slid away at once into the dark without a sound. There was no horse. ... It seemed to make up off the road, eastward. ... I tried to follow. Of course, it vanished almost at once; but I went round the corner and on as far as the last house on the Road. ... I could hardly help myself. I seemed to be drawn somehow. Anyway, I went, and suddenly I heard voices by the hedge. One was muttering; and the other was whispering, or hissing. I couldn't hear a word that was said. I did not creep any closer, because I began to tremble all over.Then I felt terrified, and I turned back, and was just going to bolt home, when something came behind me and I... I fell over.'
"'I found him, sir,' put in Nob. '...I went down to West-gate, and then back up towards South-gate. Just nigh Bill Ferny's house I thought I could see something in the Road. I couldn't swear to it, but it looked to me as if two men was stopping over something, lifting it. I gave a shout, but when I got to the spot there was no signs of them, and only Mr. Brandybuck lying by the roadside. He seemed to be asleep. 'I thought I had fallen into deep water,' he says to me, when I shook him. Very queer he was, and as soon as I had roused him, he got up and ran back here like a hare.'
"'I am afraid that's true,' said Merry, 'though I don't know what I said. I had an ugly dream, which I can't remember. I went to pieces. I don't know what came over me.'
"'I do,' said Strider. 'The Black Breath. The Riders must have left their horses outside, and asked back through the South-gate in secret. They will all know the news now, for they have visited Bill Ferny; and probably that Southerner was a spy as well." - Strider, Fellowship of the Ring, p.186

THE NAME OF ELBERETH
"At that moment Frodo threw himself forward on the ground, and he heard himself crying aloud: O Elbereth! Gilithoniel! At the same time he struck at the feet of his enemy. A shrill cry rang out in the night; and he felt a pain like a dart of a poisoned ice pierce his left shoulder." - A Knife in the Dark, Fellowship of the Ring, p.208

ALL BLADES PERISH
"Look!" he cried; and stooping he lifted from the ground a black cloak that had lain there hidden by the darkness. A foot above the lower hem there was a slash. "This was the stroke of Frodo's sword," he said. "The only hurt that it did to his enemy, I fear; for it is unharmed, but all blades perish that pierce that dreadful King. More deadly to him was the name of Elbereth." - Aragorn, "Flight to the Ford," Fellowship of the Ring, p.201

BOWS AND ARROWS USELESS
LEGOLAS: The Winged Messenger! I shot at them with the bow of Galadriel above Sarn Gebir, and I felled him from the sky. He filled us all with fear. What new terror is this?
GANDALF: One that you cannot slay with arrows. You only slew his steed. It was a good deed; but the Rider was soon horsed again. For he was a Nazgûl, one of the Nine, who ride now upon winged steeds. Soon their terror will overshadow the last armies of our friends, cutting off the sun.

NOT EASILY DESTROYED
"No," said Gandalf. "Their horses must have perished and without them they are crippled. But the Ringwraiths themselves cannot be so easily destroyed." - "Many Meetings," Fellowship of the Ring, p.236

MORGUL BLADE SHINES OF ITS OWN ACCORD
"In the dark without moon or stars a drawn blade gleamed, as if a chill light had been unsheathed." - "A Knife in the Dark," Fellowship of the Ring, p.188

THE EFFECTS OF THE MORGUL BLADE
"They tried to pierce your heart with a Morgul-knife which remains in the wound. If they had succeeded, you would have become like they are, only weaker and under their command. You would have become a wraith under the dominion of the Dark Lord; and he would have tormented you for trying to keep his Ring, if any greater torment were possible than being robbed of it and seeing it on his hand." - Gandalf, Many Meetings, Fellowship of the Ring
GANDALF: ...You were in the gravest peril while you wore the Ring, for then you were half in the wraith-world yourself, and they might have seized you. You could see them and they could see you. - Many Meetings, Fellowship of the Ring

NAZGûL MUST RIDE LIVING HORSES
FRODO: I know. They were terrible to behold! But why could we all see their horses?
GANDALF: Because they are real horses; just as the black robes were real robes that they wear to give shape to their nothingness when they have dealings with the living.
FRODO: Then why do these black horses endure such riders? All other animals are terrified when they draw near, even the elf-horse of Glorfindel. ...
GANDALF: Because these horses are born and bred to the service of the Dark Lord in Mordor. Not all his servants and chattel are wraiths! There are orcs and trolls, there are wargs and werewolves, and there have been and still are many Men, warriors and kings, that walk alive under the Sun, and yet are under his sway. And their number is growing daily. - Many Meetings, Fellowship of the Ring

ABOUT THE HORSES, WRAITH VISION AND THE SCENT OF BLOOD
"For the black horses can see, and the Riders can use men and other creatures as spies, as we found at Bree. They themselves do not see the world of light as we do, but our shapes cast shadows in their minds, which only the noon sun destroys, and in the dark they perceive many signs and forms that are hidden from us: then they are most to be feared. And at all times they smell the blood of living things, desiring and hating it. Senses, too, there are other than sight or smell. We can feel their presence - it troubled our hearts, as soon as we came here and before we saw them; they feel ours more keenly. Also, the Ring draws them." - Aragorn, A Knife in the Dark, Fellowship of the Ring

FIRE AND NAZGûL
"Sauron can put fire to his evil uses, as he can all things, but these riders do not love it, and fear those who wield it. Fire is our friend in the wilderness." - Aragorn, A Knife in the Dark, Fellowship of the Ring

FARMER MAGGOT AND THE BLACK RIDER
"'Well ... he came riding on a big black horse in at the gate, which happened to be open, and right up to my door. All black he was himself, too, and cloaked and hooded up, as if he did not want to be known.
"...''Good-day to you!' I says, going out to him. 'This lane don't lead anywhere, and wherever you may be going, your quickest way will be back to the road.' I didn't like the looks of him; and when Grip came out, he took one sniff and let out a yelp as if he had been stung: he put down his tail and bolted off howling. The black fellow sat quite still.
"''I come from yonder,' he said, slow and stiff-like, pointing back west, over my Fields, if you please. 'Have you seen Baggins?' he asked in a queer voice, and bent down towards me. I could not see any face, for his food fell down so low: and I felt a sort of shiver down my back. But I did not see why he should come riding over my land so bold.
"''Be off!' I said. 'There are no Bagginses here. You're in the wrong part of the Shire. You had better go back west to Hobbiton - but you can go by the road this time.'
"''Baggins has left,' he answered in a whisper. 'He is coming. He is not far away. I wish to find him. If he passes will you tell me? I will come back with gold.'
"''No you won't,' I said. 'You'll go back where you belong, double quick. I give you one minute before I call all my dogs.'
"'He gave sort of a hiss. It might have been laughing, and it might have not. Then he spurred his great horse right at me, and I jumped out of the way only just in time. I called the dogs, but he swung off, and rode through the gate and up the lane towards the causeway like a bolt of thunder.'" - Farmer Maggot, "A Shortcut to Mushrooms," Fellowship of the Ring, p.103-104

THE GAFFER AND THE BLACK RIDER
"It was like this: when I got back to our hole yesterday evening with the key, my dad, he says to me: Hallo, Sam! he says. I thought you were away with Mr. Frodo this morning. There's been a strange customer asking for Mr. Baggins of Bag End, and he's only just gone. I've sent him on to Bucklebury. Not that I liked the sound of him. He seemed mighty put out, when I told him Mr. Baggins had left his old home for good. Hissed at me, he did. It gave me quite a shudder. What sort of fellow was he? says I to the Gaffer. I don't know, says he; but he wasn't a Hobbit. He was tall and black-like, and he stooped over me. I reckon it was one of the Big folk from foreign parts. He spoke funny." - Sam, "Three is Company," Fellowship of the Ring, p. 85

THE ELUSIVE SCENT
"Round the corner came a black horse, no hobbit-pony but a full-sized horse; and on it sat a large man, who seemed to crouch in the saddle, wrapped in a great black cloak and hood, so that only his boots in the high stirrups showed below; his face was shadowed and invisible.
"When it reached the tree and was level with Frodo the horse stopped. The riding figure sat quite still with its head bowed, as if listening. From inside the hood came a noise as of someone sniffing to catch an elusive scent; the head turned from side to side of the road." - "Three is Company," Fellowship of the Ring, p. 84

KHAMûL AT THE BUCKLEBURY FERRY
"On the far stage, under the distant lamps, they could just make out a figure: it looked like a dark black bundle left behind. But as they looked it seemed to move and sway this way and that, as if searching the ground. It then crawled, or went crouching, back into the gloom beyond the lamps." - "A Conspiracy Unmasked," Fellowship of the Ring, p.109

THE MESSENGER TO THE LONELY MOUNTAIN
"Then about a year ago a messenger came to Dáin, but not from Moria - from Mordor: a horseman in the night, who called Dáin to his gate. The Lord Sauron the Great, so he said, wished for our friendship. Rings he would give for it, such as he gave of old. And he asked urgently concerning hobbits, of what kind they were, and where they dwelt. 'For Sauron knows,' said he, 'that one of these was known to you on a time.'
"'At this we were greatly troubled, and we gave no answer. And then his fell voice was lowered, and he would have sweetened it if he could. 'As a small token only of your friendship Sauron asks this,' he said: 'that you should find this thief,' such was his word, 'and get from him, willing or no, a little ring, the least of rings, that once he stole. It is but a trifle that Sauron fancies, and an earnest of your good will. Find it, and three rings that the Dwarf-sires possessed of old shall be returned to you, and the realm of Moria shall be yours for ever. Find only news of the thief, whether he still lives and where, and you shall have great reward and lasting friendship from the Lord. Refuse, and things will not seem so well. Do you refuse?'
"'At that his breath came like the hiss of snakes, and all who stood by shuddered, but Dáin said: 'I say neither yea nor nay. I must consider this message and what it means under its fair cloak.'
"'Consider well, but not too long,' said he.
"'The time of my thought is my own to spend,' answered Dáin.
"'For the present,' said he, and rode off into the darkness.
"'...Twice the messenger has returned, and has gone unanswered. The third and last time, so he says, is soon to come, before the ending of the year." - Glóin, "The Council of Elrond," Fellowship of the Ring, p. 254

While The History of Middle-earth is a compilation of Tolkien's earliest drafts and many things changed between the first writings and the published books, still he retained much in the final versions and often kept in mind these unpublished ideas in rejected drafts or hastily written notes.

VISIBLE CLOTHING; INVISIBLE BODY
"This ends a sheet, and the following sheet is not continuous with what precedes; but as found among my father's papers they were placed together, and on both of them he wrote (later) 'About Ring-wraiths.' The second passage is also part of a conversation, but there is no indication of who the speaker is (whoever it is, he is obviously speaking to Bingo). It was written at great speed and is extremely difficult to make out.

"Yes, if the Ring overcomes you, you yourself become permanently invisible - and it is a horrible cold feeling. Everything becomes very faint like grey ghost pictures against the black background in which you live; but you can smell more clearly than you can hear or see. You have no power however like a Ring of making other things invisible: you are a ringwraith. You an wear clothes. [>you are just a ringwraith; and your clothes are visible, unless the Lord lends you a ring.] But you are under the command of the Lord of the Rings."

On this passage Christopher Tolkien added this footnote: "My father first wrote here that the clothing of one who has thus become permanently invisible was invisible also, but rejected the statement as soon as written."
- "Of Gollum and the Ring," The Return of the Shadow, page 74-75; footnote on page 84

GANDALF THE WHITE AND THE POWER OF THE RINGWRAITHS
"Gandalf to reappear again. How did he escape? This might never be fully explained. He passed through fire - and became the White Wizard. 'I forgot much that I knew, and learned again much that I had forgotten.' He has thus acquired something of the awe and terrible power of the Ring-wraiths, only on the good side. Evil things fly from him if he is revealed - when he shines. But he does not as a rule reveal himself."
- Notes on Various Topics, The Treason of Isengard, p. 422

HOW TOLKIEN IMAGINED MINAS MORGUL
In 1969, J. R. R. Tolkien collaborated with artist Pauline Baynes to create a map of Middle-earth. Baynes' map can easily be found through image searches, although one should keep in mind that there are two versions of the map circulating the internet. The original version of the map has a drawing of the Fellowship of the Ring on the top, and a drawing of orcs, Gollum, the Nazgûl, and Shelob on the bottom. However, a cropped version of the map also exists. The following quote refers to the full version of the image.

On seeing the finished art, Tolkien wrote a set of comments on these depictions of places and characters. Some of these comments are appreciative: e.g. Tolkien found four of the vignettes, sc. Those depicting the Teeth of Mordor, the Argonath, Barad-dûr, and Minas Morgul, particularly well-executed, and described them as agreeing "remarkably with my own vision… Minas Morgul is almost exact […]"
--"Character Descriptions," The Nature of Middle-earth, edited by Carl F. Hostetter, p. 190.

NOTE: "The Tower of the Moon" by Ted Nasmith bears many similarities to Bayne's version.

A GLOWING CITY WITH A REVOLVING TOWER
Now, feeling the way become steep before his feet, he [Frodo] looked wearily up; and then he saw it, even as Gollum had said that he would: the city of the Ringwraiths. He cowered against the stony bank.
A long-tilted valley, a deep gulf of shadow, ran back far into the mountains. Upon the further side, some way within the valley's arms, high on a rocky seat upon the black knees of the Ephel Dúath, stood the walls and tower of Minas Morgul. All was dark about it, earth and sky, but it was lit with light. Not the imprisoned moonlight welling through the marble walls of Minas Ithil long ago, Tower of the Moon, fair and radiant in the hollow of the hills. Paler indeed than the moon ailing in some slow eclipse was the light of it now, wavering and blowing like a noisome exhalation of decay, a corpse-light, a light that illuminated nothing. In the walls and tower windows showed, like countless black holes looking inward into emptiness; but the topmost course of the tower revolved slowly, first one way and then another, a huge ghostly head leering into the night.
--"The Stairs of Cirith Ungol," The Two Towers, p. 312

THE MEADS OF CHARNEL FLOWERS
So they came slowly to the white bridge. Here the road, gleaming faintly, passed over the stream in the midst of the valley, and went on, winding deviously up towards the city's gate: a black mouth opening in the outer circle of the northward walls. Wide flats lay on either bank, shadowy meads filled with pale white flowers. Luminous these were too, beautiful and yet horrible of shape, like the demented forms in an uneasy dream; and they gave forth a faint sickening charnel-smell; an odour of rottenness filled the air. From mead to mead the bridge sprang. Figures stood there at its head, carven with cunning in forms human and bestial, but all corrupt and loathsome. The water flowing beneath was silent, and it steamed, but the vapour that rose from it, curling and twisting about the bridge, was deadly cold. Frodo felt his senses reeling and his mind darkening.
--"The Stairs of Cirith Ungol," The Two Towers, p. 313

MORGUL LIGHTNING
And Minas Morgul answered. There was a flare of livid lightnings: forks of blue flame springing up from the tower and from the encircling hills into the sullen clouds. The earth groaned: and out of the city there came a cry. Mingling with harsh high voices as of birds of prey, and the shrill neighing of horses wild with rage and fear, there came a rending screech, shivering, rising swiftly to a piercing pitch beyond the range of hearing.
--"The Stairs of Cirith Ungol," The Two Towers, p. 315

THE CITY'S GATE RESEMBLES A GAPING MOUTH
As the terrible cry ended, falling back through a long sickening wail to silence, Frodo slowly raised his head. Across the narrow valley, almost on a level with his eyes, the walls of the evil city stood, and its carnivorous gate, shaped like an open mouth with gleaming teeth, was gaping wide. And out of the gate an army came.
--"The Stairs of Cirith Ungol," The Two Towers, p. 315
NOTE: Tolkien drew a picture of the gate of Minas Morgul, which can be found on page 342 of The Treason of Isengard.

MORE ABOUT THE CITY'S GATE
Minas Morgul must be made more horrible. The usual "goblin" stuff is not good enough here.
The Gate shaped like a gaping mouth with teeth and a window like an eye on each side. As Sam passes through he feels a horrible shudder. There are two silent shapes sitting on either side as sentinels.
--"The Story Forseen From Lorien," The Treason of Isengard, p. 340.
NOTE: In this earlier draft, the scenes that would later be set in Cirith Ungol are set in Minas Morgul instead; hence the reference to the Silent Watchers.

THE STREETS OF MINAS MORGUL
NOTE: In this early draft, Frodo is taken to Minas Morgul after being bitten by Shelob, and Sam rescues him. Together they must find a way to sneak out of the city.
Now they issued from the Loathly Tower. Evening was falling: away in the West over the valley of the Anduin there was some light. Far away loomed the Black Mountains and the tower of Minas Tirith, had they known. But in the East the sky was dark, with black and lowering clouds that seemed almost to rest upon the land. An uneasy twilight lay in the shadowy streets. Shrill cries came as it were from underground, strange shapes flitted by or peered out of alleys and holes in [gaping] houses; there were [dispirited] voices and faint echoes of monotonous and unhappy song. All the carven faces leered, and their eyes glowed with a fire at great depth.
The hobbits shuddered as they hurried on. Feet seemed to follow them, and they turned many corners, but they never threw them off. Rustling and pattering on the stones they came doggedly after them.
They came to the gates. The main gates were closed; but a small door was still open. Sentinels stood on either side, and at the opening stood an armed warder, gazing out into the gathering dust. The Orcs were waiting for the messenger from Baraddur.
--"The Story Foreseen from Lorien," Treason of Isengard, 336-7.