Nagashizzar is the fortress city of Nagash, the Great Necromancer constructed within Cripple Peak near the Sour Sea, surrounded by the Desolation of Nagash and in the Worlds Edge Mountains, underneath which lies the "Cursed Pit". Nagash let his Undead minions built a vast fortress here after discovering the presence of a huge chunk of warpstone around -1600 IC. Drawn to the warpstone, the Skaven tried to infiltrate the Cursed Pit. The two, Skaven and Nagash, dominate the events at Nagashizzar.
Cripple Peak is a giant mountain at the shore of the Sour Sea which has been split in two after a piece of warpstone plummeted from the sky into the peak. The area around has been corrupted by the foul warpstone. Within the mountain extended a vast labyrinth of caves. Nagashizzar, the fortress city, was sculpted and excavated from the mountain. It highest spire, the mountain top, rises nearly half a mile over the surrounding desert, the Desolation of Nagash.
Nagashizzar is a fortified mountain, within countless leagues of corridors, a multitude of chambers and the most horrofying Undead things which dwell within. Alchemical laboratories, barracks, foundries and armouries and the largest library of necromantic lore. Hundreds of great towers bristle from the mountain side and four gates guard the city's entrances, protected by golems of bone, bolt throwers and catapults. The gates are black.
There is a great throne room where upon a pile of skulls is placed Nagash's throne. The Great Necromancer's husk is said to be seated there, brooding for more than a millennium. From here he is conscious of all what happens within the city and steers the puppets that are its undead inhabitants if necessary. There are also living beings within Nagashizzar: disciples of Nagash who sought him to learn more about Necromancy and cultists who worship him as a god and await his arising. Their activity can be seen as green witchlights flicker behind windows at night.
The city is Nagashizzar, the mines beneath are called the "Cursed Pit" a honeycomb which extends almost twice as deep as the mountain is high. They were excavated by Undead and Skaven alike to mine for warpstone, which is by now almost exhausted.
In ancient times a huge chunk of warpstone plummeted from the sky and bore itself into Cripple Peak, splitting the mountain in two and boring itself into the earth beneath. Ever since, the surrounding has been fouled. The primitive human tribes which lived at its sides were not spared from its mutating effects.
Around -1600 IC, after he had been driven out of Khemri and he had wandered around, Nagash finally found a place to stay and he occupied the caves in the side of Cripple Peak for many years as a hermit, meditating about the dark art and experimenting with the powers of the warpstone which he found deep in the mountain. Using the dead from the local tribes, he rose undead workman to excavate a huge fortress. Later he enslaved the living tribesmen, who had started to worship Nagash as a god, to work at their sides. Within a few hundred years, the fortress city Nagashizzar was built and Nagash ruled an empire of evil along the shores of the Sour Sea. The warpstone was excavated and a labyrinth of mines, the Cursed Pit, was created. Villages grew into towns and fortifications were erected.
Skaven, drawn to the warpstone, burst into the mines in -1350 IC, but found the animated corpses and living human fanatics difficult opponents. For a century they fought, but Nagash had other plans and didn't want to be distrated by the Skaven, so he made a pact with the Skaven#Council of Thirteen. In return for Greenskin slaves, the Skaven were allowed to access the warpstone. The mining spread more warpstone dust than ever before and the humans who lived from the animals who ate the plants who used the water which was poisoned by warpstone degenerated into Ghouls.
Around -1200 IC and the years afterwards, the Vampires whom escaped the purge of Lahmia arrived at Nagashizzar, uniting with their god, Nagash. Arkhan the Black arrived too. From Nagashizzar, they led an army of undead against King Alcadizaar of Nehekhara, but were defeated and returned to Nagashizzar. The vampires blamed each other, fought and disappeared out of the city, except for Wsoran who would lead a second attack on Nehekhara. This time they were victorious and Alcadizaar was brought back and imprisonned in the dungeons of the Cursed Pit. In -1151 IC, Nagash prepared for the Great Ritual, but Alcadizaar was freed by the Skaven and killed Nagash before the foul ritual was done. Alcidizaar grabbed the Crown of Sorcery and fought his way free from the fortress. Wsoran, who had been studying necromantic lore in Nagashizzar, fled, taking one of the "Nine Books of Nagash".
With Nagash gone, the Skaven had free access to the warpstone and plundered it during the following millenia untill almost exhausted, though the place was not rid of the dark powers and undead remained to inhabit the cursed place. Leaderless they were no match for the Skaven.
Vorag Bloodytooth united the Ghouls under his banner around -600 IC and led them out of Nagashizzar. Some years later, the remnants of his defeated army of Ghouls returned to the fortress city.
In -40 IC Nagash was reborn and returned to Nagashizzar, driving out the remaining Skaven in a single night. During the next decades they battled once more over control of the mines untill Arkhan the Black returned in -15 from his wandering in Araby and devastated the Skaven at the Battle of Death Rock. The Ratmen retreated. In search of the Crown of Sorcery, Nagash soon left himself.
What happened in the following centuries with Nagashizzar is unknown, but in 1681 IC Nagash was reborn in the Black Pyramid at Khemri and returned to his fortress to dwell within, gathering his strength.