The Blackstone Fortresses were originally created as Warp-based weapons that were used in the first war by the Old Ones against the C'tan and the Necrons known as the War in Heaven. They were known to the ancient Eldar as the Talismans of Vaul. To capitalise on the C'tan's vulnerability to warp attacks the Fortresses were equipped with a Warp Cannon that could create a devastating rip in space and an eruption of energy out of the Immaterium, powerful enough to destroy entire star systems. They have since fallen into the use of the Imperium and Chaos, and have influenced two of the most recent Black Crusades of Chaos against the Imperium. It is believed that all but one of the Blackstone Fortresses has been destroyed, and that fortress has been possessed by the essence of the Chaos God Slaanesh since the end of the 13th Black Crusade in 999.M41.
The Blackstone Fortresses were a collection of six massive and mysterious artefacts of pre-Imperial culture that were scattered across the Gothic Sector in the Segmentum Obscurus. Each was a vast installation whose mass was larger than even the mightiest Imperial starforts and segmentum fortresses. Imperial archaeo-historians place the construction of these ancient artefacts anywhere between 17,000 and 300,000 years before their discovery in the 33rd Millennium (though some scholars estimate them to be far older). For as long as the Imperium has been aware of their existence, the Blackstone Fortresses lay in a dormant state, with all but passive power systems shut down despite their best efforts to revive them. Although inactive, there was enough residual power in their power grids to allow the humans to live in them and turn them into powerful spaceborne hardpoints that were central to the fortifications in the systems they occupied. The Blackstone Fortresses became the foundation of the Imperial Navy strategy and presence in the Gothic Sector. With the exception of Port Maw, each sub-sector was based upon the location of a Blackstone Fortress, which functioned as the primary naval base for the sub-sector. Although almost entirely dormant, a Blackstone Fortress was still open to exploitation by Imperial forces. The Adeptus Mechanicus linked numerous weapon systems to its alien and near-incomprehensible energy grid, opened up vast chambers to be used as attack craft launch bays and installed defence turrets over its surface.
Gothic War (12th Black Crusade)
During the Gothic War, Abaddon the Despoiler was influenced by the C'tan known as 'The Deceiver' to find a pair of ancient devices, (known as the Hand of Darkness and the Eye of Night, probably Eldar devices with some kind of command code or password) which re-activated the massive ships, bringing them under his control. Thought impregnable by the Imperial Navy, the Blackstone Fortresses were overcome by Abaddon using a previously undiscovered method of shutting down the power supply, thus rendering all the weapons and defence turrets useless. Once deactivated, the Blackstone Fortresses were defenceless against ranged attacks and almost undefendable against a determined boarding action. Once awaken the Blackstone Fortresses were able to shed their grafted-on Imperial equipment and glide slowly through space under their own power, using their original warp-cannon in place of the turrets and fighter bays the Imperial Navy had built onto them. There is also a record of a boarding party that made its way into one of the activated fortresses and described it as like a living thing, pulsing with power. As the war progressed and Abaddon acquired three Fortresses, he was able to combine their warp-cannon attacks to obliterate worlds and stars. The Blackstone, like most Eldar technology of that scale was equipped with an Infinity Circuit of some kind. However, when it fell into the hands of Chaos, it was corrupted and possessed directly by the Chaos God and enemy of the Eldar, Slaanesh.
At the end of the Gothic War, the fortresses were attacked by a vast fleet of Imperials and Eldar over the world of Schindelgheist, and Abaddon retreated into the Eye of Terror with two activated Blackstones, while the remaining Blackstone was re-captured. When the aforementioned boarding party boarded the Blackstone Fortress, the remaining three in Imperial custody simultaneously disintegrated.
13th Black Crusade
During the 13th Black Crusade, Abaddon the Despoiler used the two Blackstone Fortresses he had captured during the Gothic War against the Imperium of Man's defenders. One of these was used to attack the world of Cadia, obliterating Cadians and Chaos troops on the surface indiscriminately. This Blackstone Fortress was attacked by Eldar and Imperial battlefleets, but both took huge losses from the Chaos warfleet guarding the structure. The great Eldar Farseer Eldrad Ulthran boarded the fortress, attempting to remove the taint of Chaos and return the fortress to Eldar control. As the fortress had been possessed by a portion of the mind of the Chaos God Slaanesh, Eldrad's body was destroyed, but his mind remains trapped within the construct. After Eldrad's assault, the fortress stopped attacking Cadia and concentrated on its own defence. It was later attacked by a Necron fleet, which was attempting to destroy the greatest weapon of their ancient enemies, the Old Ones. The Necron fleet failed in this effort and was destroyed, but it caused enough damage to the fortress that it finally retreated from Cadia and back into the Eye of Terror.
There are unconfirmed reports of the other Blackstone Fortress in the hands of the Forces of Chaos being destroyed by similar Necron raiders.
Viewed from the top the shape of an activated Blackstone Fortress has warped to resemble the eight-pointed star of Chaos Undivided (this is somewhat ironic considering the fortresses are of Old Ones' creation).
Capabilities & Technology
In terms of capability and technology the Blackstone Fortresses beggared belief -- able to glide sedately through the void with no obvious means of propulsion and seemingly able to ignore the laws of inertia, their shielding and armor were several times that of the greatest battleship, and their weaponry harnessed warp technology to unleash a beam of purest Immaterium with the power to obliterate any capital ship at extreme range in a single volley, and even more terribly could be combined with one another. Two Blackstone Fortresses could strip a world of its biosphere in an eyeblink, and three could destabilize a star. The builders of these technical marvels are a mystery, there has been suggested that they were constructed by the Eldar for use in their ancient war with the C'tan, indeed they are obliquely mentioned in Eldar myth as objects of fear and revulsion, and Farseer Eldrad Ulthran himself deemed them such a threat that when they fell into the hands of Chaos, he sacrificed himself in a desperate bid to wrest one from its control. Yet the Blackstone Fortresses also exhibited technology, such as void shielding and apparently inertia-less propulsion, which was very different from that used by the Eldar. The Blackstone Fortresses mastery in manipulating the warp, demonstrated in their weaponry, far surpassed even that of the Eldar, the acknowledged masters of warp technology in the galaxy.
Similarly, while the Blackstone Fortresses exhibit some aspects eerily similar to Necron technology in both function and appearance they were also puzzlingly different in their use of mighty void shields and their direct manipulation and utilization of warp energy, something that the C'tan regarded as anathema. Further detracting from this theory is the fact that there are strong hints that the manipulations of the enigmatic C'tan known as 'The Deceiver set the Gothic War in motion to ensure the scattering and/or destruction of these artifacts. Several other points are worth noting, first that whatever and whomever caused the destruction of four of the Blackstone Fortresses at the close of the Gothic War must have done so consciously and it was Inquisitor Lord Horst's belief that someone or something had deemed them to great a threat to continue to exist. Second, if the hazy account of Eldrad's final gambit is to taken at face value then the Blackstones possess some sort of "psychic matrix" and a will of their own.
Finally, it is worth noting that the Blackstone Fortresses seem on most respects similar to the unspeakably ancient and mysterious Fortress Worlds of the Sabbat Worlds, positively dated back to at least eight million years of use by successive species in much the same way as the Blackstones were. Taken together, these facts suggest that the Blackstone Fortresses are but some remnants of an ancient and technologically advanced species scattered across the galaxy. As the capabilities of the Fortresses make them ideally suited to do battle with the Necrons it is reasonable to suspect that they are yet another leftover from that primordial conflict between the Old Ones and C'tan, although given the dates for construction that Imperial experts attached to them and similar structures, it is equally likely that such an apparent connection is merely illusory and their origins are not directly related to that conflict. If this is the case, it suggests the existence at some point of a vast and previously unknown empire of a very technologically advanced species, this of course would generate only more questions.
If Imperial estimates are incorrect and they are in fact relics of that bygone age of conflict then their most likely architects may be the Old Ones themselves, who were said to command the Warp in ways that their successors could only dream of, they might be the remnants of that species defenses against the C'tan advance. If the Eldar myth-history of their gods are in fact a distortion and amalgamation of the race-memories of the Old Ones and the actions of the psychic beings which came into being through Eldar faith and dim recollection of their original creators as the so-called "Talismans of Vaul," perhaps the Blackstone Fortresses are equated with the story of the 100 Swords of Vaul forged for bloody-handed god Khaine, and that the actual weapons forged in ancient times by and Old Ones which informed the subsequent myth of the Eldar War in Heaven.
- Battlefleet Gothic Rulebook, pp. 78, 95-97, 100-102, 127, 140, 145, 159
- Codex: Eye of Terror (3rd Edition)
- The Sabbat Worlds Crusade (Background Book)
- The Thirteenth Black Crusade (Background Book)