The blackstone fortresses was a galactic-wide system of incredibly powerful naval bases created by the Eldar and then harnessed by Humanity, presumably in the dark age of technology. with the religious crackdown on knowledge and technology, the skills needed to operate these vast defences were lost, only to have been awakened by Chaos lord Abaddon during the black crusades using millenia old relics. it is widely believed that he destroyed two of these stations and returned to the warp, causing the millions of others controlled by Cadia command to be garrisoned with Space Marine and Inquisitor forces.

When activated in tandem, they can join energy beams into one larger enough to eliminate sectors with, which poses a very real threat to all enemeis of Mankind.