Sotha - Horus Heresy: Barabas Dantioch, a former Warsmith of the traitorous Iron Warriors, who remained staunchly loyal to the Emperor once the Horus Heresy began, was recruited by Roboute Guilliman for his skills in the arts of siegecraft. Dantioch and his Loyalist compatriots of the IVth Legion managed to arrive in the Realm of Ultramar before the Battle of Calth was initiated by the treacherous Word Bearers Legion.During the Traitors' assault on that world, the Dark Apostle Erebus managed to complete a blasphemous ritual on Calth's surface which summoned a phenomenon called the "Ruinstorm" to the galaxy's Eastern Fringe -- a monstrous Warp Storm larger and more destructive than anything space-faring Humanity had witnessed since the days of the Age of Strife.It was intended to split the void asunder, dividing the galaxy in two and rendering vast tracts of the Imperium impassable. The Five Hundred Worlds was rendered unnavigable except for the most high-risk enterprises. Imperial trade and communication in the region collapsed.Ultramar, as a single and admirable area of Imperial governance, was ruined. The Ruinstorm would also isolate and trap those Loyalist forces caught behind it like the Ultramarines, preventing them from coordinating their efforts and supporting one another as the Traitor Legions moved towards Terra.Dantioch had supposed that he would be employed in fortifying the physical defences of Macragge and other key worlds of Ultramar, for this was his forte. Then Roboute Guilliman had revealed to him the long-sequestered mysteries of Sotha, and Dantioch had realised that the survival of a pocket empire like Ultramar lay less in fortifying its physical defences and far, far more in strengthening its function and operation.Dantioch spent over nine solar months unlocking Sotha's mysteries and activating the planet's deep-time secrets. Dantioch agreed absolutely with the Ultramarines primarch's assessment -- Sotha offered a way in which the Loyalists might overcome the Ruinstorm, rather than simply batten down against its wrath.Dantioch and the Ultramarines descended into the vast chambers of the Pharos on pre-fabricated walkways of STC design to provide platforms, ladders, stairs and bridges that would allow Humans to traverse and explore the almost endless interior of the Pharos.During their explorations they discovered a central chamber, later known as "Primary Location Alpha," which Dantioch was convinced was the centre of the entire mechanism. Dantioch took to referring to it in his notes as the "tuning stage" or the "sounding board".He had been fairly confident that he understood the function of the Pharos even from the data he had studied before his arrival on Sotha. The Pharos was part of an ancient interstellar navigation system, both a beacon and route-finder, and it also permitted instantaneous communication across unimaginable distances.Unlike Imperial Warp technology that used the Immaterium to by-pass realspace, the quantum function of the Pharos once allowed for site-to-site teleportation, perhaps through a network of gateways. Its fundamental function lay not with psychic energy like Imperial FTL technology, but with empathic power.Dantioch also believed that other way stations like the Pharos still existed, or once did, on other worlds throughout the galaxy. It was not one, single beacon like the Astronomican. Dantioch believed the Pharos and other stations like it were once used to create a network of navigational pathways between stars, as opposed to a single, range-finding point the way the Astronomican did. The Pharos was more like a lantern than a beacon.The Pharos could be tuned and pointed, illuminating a site or location for the benefit of range-finding. Though Roboute Guilliman was loathe to use xenos technology, Ultramar had to be held together, and to rebuild the Five Hundred Worlds, the Loyalists had to restore communication and travel links by piercing and banishing the current age of darkness.Utilising the Pharos' strange abilities, Dantioch was able to illuminate Macragge, lighting it up as a bright spot that was visible throughout realspace and the Warp, despite the effects of the Ruinstorm, providing a directional beacon for navigation in the absence of the Astronomican.