The Black Library of Chaos, also known simply as the Black Library, is the secret Aeldari Craftworld that serves as the Aeldari's repository of forbidden lore concerning the Ruinous Powers that exists somewhere within the labyrinthine passages of the Webway. The Aeldari Craftworlds became the only surviving sources of their ancient knowledge of sorcery and the Ruinous Powers of Chaos after the Fall of that species to the birth of Slaanesh.
As the Craftwords have drifted apart, this knowledge has consequently become fragmented, and as some Craftworlds have become lost over the millennia, more precious Aeldari knowledge has been lost with them. The Black Library is governed by a body of the wisest Asuryani Farseers drawn from all of the Craftworlds known as the "Black Council." The Black Council is the closest the fractious Aeldari species has come to an advisory body that looks after the interests of the entire race.
The Aeldari know more of Chaos than mankind ever will, and still more was lost during the Fall. A single source of Aeldari knowledge has remained untouched and inviolate since the Fall. In a hidden location, some say at the very centre of the Webway -- the Aeldari's network of stable Warp tunnels that crosses the galaxy -- rests the tomes, books, scrolls, and codices describing the Aeldari's complete and extensive knowledge of the Warp. The forbidden lore of the Black Library describes the blandishments, influences, forms, creatures, perils, promises, and horrors of Chaos.
The existence of the Black Library is known to only a few and entry is allowed to even fewer individuals. The library defends itself against the weak and those who would misuse its knowledge by refusing entry to all except those who have acknowledged and tempered the Chaos within themselves. The immature, who are still vulnerable to the promises and seductions of Chaos, find that they are unable to pass through its gateway. As a result, only the Solitaires of the Aeldari Harlequin troupes are allowed to come and go freely, although some say that a human, perhaps an Inquisitor, has also been allowed to do so.
The Black Library is the only source of the Aeldari's knowledge concerning Chaos that has remained untouched. It was created by the Aeldari deity Cegorach, better known as the Laughing God, though for what purposes the god created this repository can only be guessed. The Black Library is spoken of by the Aeldari as a dark Craftworld existing within the Webway, far beyond the reach of the Imperium of Man.
Within are the collected tomes and writings describing the Aeldari's studies of the Immaterium and all the entities that live within it. These writings also describe all aspects of Chaos: its perils, promises and horrors. The Library is enclosed within a nearly impenetrable psychic barrier, and is watched and maintained by its Aeldari Guardian-Scribes, who collate and transcribe the knowledge of the Black Library, a task they have carried out since the Fall.
The Black Library contains not just the Aeldari's knowledge of Chaos; any new knowledge of Chaos gained by any intelligent species of the galaxy is taken and kept within the Library. These include a copy of the Book of Magnus, the potent tome of sorcery created by the Thousand Sons Traitor Legion's Primarch or the Book of Lorgar written by the Primarch of the Word Bearers Traitor Legion that sought to spread the teachings of the Ruinous Powers, both before the Horus Heresy.
The Black Library is as much a source of knowledge for those who fight Chaos as it is a vault to keep dangerous knowledge hidden and protected from those who would misuse it. The existence of the Black Library is known to few, and even fewer are allowed access to it. The Library's collective psychic mind embodied in its Infinity Circuit defends itself, barring the weak and corruptible. Only those who have mastered the temptations of Chaos within themselves are able to enter.
Two groups come and go at will: the human Illuminati and the Aeldari Solitaires, the most dangerous of the Harlequins. The Imperial Inquisitor Bronislaw Czevak was granted entry by the Black Council once to study the accumulated lore concerning Mankind's interaction with Chaos, but had to prove himself worthy of the honour.
The Chaos Sorcerer Ahriman of the Thousand Sons Traitor Legion sought entrance to the Library in his vain attempt to better understand his master, the mercurial Tzeentch, the Changer of the Ways and the Chaos God of Sorcery. For many Terran centuries the Black Library and its guardians managed to repel this particularly troublesome would-be invader.
Then in 998.M41, shortly before Abaddon the Despoiler's 13th Black Crusade began, Ahriman led his warband of Thousand Sons into the Webway in an effort to finally claim the Black Library. Engaging in furious battles with the Harlequins and the forces of the Craftworlds of Ulthwé and Lugganath, Ahriman advanced to within sight of the Library itself. However, several major arteries of the Webway were choked with the dead before the Heretic Astartes were driven from the secret paths leading to the Library. The breach caused by the rampaging sorcerers was sealed, but as a result, a section of the Webway was lost forever to the Aeldari.
The Final Act
At the very heart of the Black Library, there lies a silver-lit vault. Therein stands a plinth made of finely graven obstinite, upon which rests a crystalline book said to contain the words of the Aeldari god Cegorach himself. Since the Fall, the tome's covers have remained closed, sealed shut with flickering chains of light. Yet now, long-awaited portents have come to pass. A fallen sorcerer sought and nearly won the lore of the library. A king stirred back to life in his court of death and silence, and rose once more to lead Mankind. As the signs of the Rhana Dandra have come to pass, so the bands of light about the tome have flickered and died.
Now, at last, the tome has fallen open following the birth of the Great Rift. Within its pages the Shadowseers have found a script, a secret final act that changes utterly the tale of the Fall. Penned in inks of light and shadow, these words present a slender hope, detailing an intricate, galaxy-spanning performance with the potential to change the fate of the Aeldari species.
Always, the strands of fate have pointed toward the victory of Chaos during the last, mythic battle of Creation known to the Aeldari as the Rhana Dandra. Yet within the pages of the crystal tome is recorded Cegorach's ultimate jest, a way to trick Slaanesh into expending all her power not to destroy the Aeldari, but to save them.
How such an impossibility could come to pass is unclear, for on this matter the final act is infuriatingly vague. Yet the Harlequins take their god's words on faith alone, for their devotion to Cegorach is total and his methods beyond question or reproach. Thus they have begun the steps of this final dance, and will see it completed, or else face absolute destruction in the attempt.
The Black Library is a "dark" Craftworld eternally travelling through the Webway. Its location and route are secret, hidden from all but the Harlequins and the members of the governing Black Council. Like all Craftworlds, the vessel is conscious and psychoactive, hiding itself from all psychic probes, while simultaneously repelling Warp entities and intrusions.
It is an enormous construct with a scorched, crystalline appearance, covered in vanes and flourishes but with the typical flowing grace of Aeldari architecture. The interior is an intentional labyrinth with all manner of convoluted passages, corridors, and chambers. Bubble vaults full of stasis caskets containing forbidden lore and dangerous artefacts hang from the superstructure, whilst inside and above are myriad citadels, obelisks, monoliths, and spires where the rest of the Craftworld's arcane contents are kept.
Among the varied structures present within the Black Library is the Wraith Tower, the section of the Library devoted to humanity's interaction with Chaos, the accumulated lore of the Imperial Traitors. The psychic emanations of the Webway are known to have a regenerative effect upon human tissue, which greatly benefited the human Inquisitor Czevak. Several standard years after he was granted permission to study at the Black Library, a much younger-looking Czevak returned to realspace and the Imperium, no longer needing the assistance of his cryogenic suspension suit to easily move his once-aged body around.
- Codex: Harlequins (8th Edition), pp. 14-15
- Codex: Eldar (6th Edition) (Digital Edition), "The Doom of the Eldar"
- Warhammer 40,000: Compendium (2nd Edition)
- Realm of Chaos: Slaves to Darkness, pg. 215
- Realm of Chaos: The Lost and the Damned
- Harlequin (Novel) by Ian Watson
- Xenology (Background Book)
- Atlas Infernal (Novel) by Rob Sanders