The Cults of the Thousand Sons represented sub-formations composed of potent psykers within the Thousand Sons Space Marine Legion first created during the Great Crusade era who specialised in certain psychic and sorcerous disciplines. The Thousand Sons, like some of their fellow independent-minded Astartes Legions, employed a non-standard organisation within the XV Legion that were known as Cults and into which every Astartes was placed based upon their level of psychic ability.
After the fall of the Thousand Sons to the service of Tzeentch during the Horus Heresy and the transformation in the Legion wrought by the casting of the Rubric of Ahriman, the five cults of the original Legion became nine. With this new Legion structure, the Sorcerers of the Legion delved more deeply into the true secrets of the Lord of Change and were guided by the will of their Daemon Primarch, Magnus the Red.
Though some Thousand Sons Astartes never developed any measurable amount of psychic ability after being implanted with the XV Legion's gene-seed, the majority did develop some form of psychic ability just like their Primarch Magnus the Red soon after completing the transformation process. The Legion used these five different Cults to develop and improve the abilities of the often powerful psykers found amidst this Legion's ranks. Membership within these Cults was determined regardless of the Fellowship (Chapter) to which each Astartes belonged within the Legion since Cult membership was based upon the psychic ability for which a Thousand Sons Astartes displayed the most affinity. Each Fellowship of the Thousand Sons was usually made up of Astartes coming from all five of the Cults within the XV Legion, though it was not unheard of for a Fellowship's membership to be dominated by the members of just one of the Cults.
The five Cults had been founded within the Legion by the nine original members of Magnus the Red's inner circle or cabal who were collectively known as the Rehati. The Rehati had each earned mastery in one of the 5 recognised psychic disciplines. Each Cult was formed to further the development of one of the recognised psychic aptitudes: the Athanaeans focused on telepathy, the Corvidae sought to develop their precognitive abilities, the Pavoni learned to make use of physiokinesis, the mental manipulation of one's own physiological processes, the Pyrae plumbed the secrets of fire, a discipline called pyrokinesis, and the Raptora mastered the potent power of telekinesis. The leader of each Cult bore the rank of Magister Templi. The leader of all the Cults was known as the Magus and this was a rank exclusively held by the XV Legion's Primarch, Magnus the Red. The highest rank within the Cult system was that of Ipissumus, a grade which represented a being free from limitations, who lives in balance with the corporeal and incorporeal universe. For all intents and purposes, the Ipisssumus was the most perfect being in the universe. This esteemed rank was represented by the most powerful human psyker in existence -- the Emperor of Mankind.
On the Thousand Sons' lost homeworld of Prospero, in the capital city of Tizca, each Cult maintained its own pyramidal headquarters, which served as both a repository of the arcane knowledge that they had collected about their chosen psychic disciplines from across the galaxy as well as training facilities specifically geared towards enhancing psykers who displayed strength in one of the five recognised psychic disciplines. Each of these pyramids' front gates was topped by the great golden icon that represented the Cult, save for the pyramid of the Pyrae Cult, which was topped by an ever-burning flame and whose gate was guarded by Canis Vertex, a Warlord-class Battle Titan of the Legio Astorum that would see action during the Burning of Prospero.
To further represent the distinctiveness of the Cults' members, the Astartes from each Cult would display the Cult's insignia upon the shoulder plates of their Power Armour, with the Cult's distinctive icon placed within the centre of the XV Legion's Pre-Heresy Legion badge. The five known cults of the Pre-Heresy Thousand Sons Legion are described below.
After the casting of the Rubric of Ahriman, the confluence of once-noble fellowships that comprised the Legion was replaced by a hierarchy born of Magnus' will. The Thousand Sons were divided into nine great cults, each devoted to a separate facet of the Change God, and whether wittingly or not these cults all serve Magnus, and all have a purpose in the unfathomable plans of Tzeentch.
Though the Planet of the Sorcerers to which the Thousand Sons were exiled after the Fall of Prospero is a world in constant flux, its inhabitants are governed by a strict order set in place by Magnus. The spectral remnants of the Legion's warriors, known as the Rubricae, reign over throngs of Chaos Cultists, Tzaangors and mutated Warp beasts, while above the Rubricae is the former bodyguard of the Crimson King, known as the Sekhmet. Raised above all of these is the Rehati -- a coven of nine Exalted Sorcerers and Daemon Princes who are favoured by Tzeentch more than any other amongst the Thousand Sons, save Magnus himself.
From this overarching hierarchy, the Legion's forces are now further divided into nine great cults. At the head of each is a member of the Rehati who bears the ancient rank of Magister Templi. Beneath each Magister Templi are nine other Daemon Princes and Sorcerers who, though lesser in rank, still bear much of Tzeentch's favour. These nine steer the cult along the ever-changing paths of fate. Other Sorcerers hold lower positions in the cult, and along with troops, tanks, mutants and Daemon Engines are capable of claiming vast swathes of realspace for their cult masters. Each cult has worlds from which they draw resources and magical energy, and populous planets to provide them with constant streams of Cultist soldiers, slaves and subjects for their arcane experiments.
Aside from constituting a terrifying military force, each of the cults is an amalgam of the twisted minds of those in its ranks, and though inherently self-serving, the members of a given cult are ultimately bent towards the same purpose. To a mortal mind, untouched by Tzeentch's corruptions, the complex plans laid out by these cults are utterly unfathomable, but to the Thousand Sons they are both a form of profane worship and a route to vengeance over the Imperium of Man. Often, the goals of a given cult will undermine or even contradict those of the other cults. As such, the cults are wary of one another, and alliances between them are ever-shifting. The power and influence of each is also in constant flux, with every cult going through cycles of activity and torpidity as befits their inscrutable machinations.
It is extremely rare for the entirety of a cult to deploy in a single war zone, though when this does happen the fabric of reality quakes in their presence. More often, the cult's malevolent goals require its forces to be spread throughout space and time, allowing each splinter to play a separate role in some larger and more sinister stratagem. A cult therefore comprises many sects, each of which may prosecute their own seemingly unconnected campaigns of terror. Where the combined forces of a cult could easily set a whole system ablaze, a single sect is still capable of devastating a planet. Often, several sects will launch simultaneous strikes across large tracts of realspace, plunging entire sub-sectors into disarray and panic. As nearby worlds send reinforcements to the embattled planets, more Thousand Sons appear to attack where defences have been stretched to breaking point. Devastating as they are, these attacks rarely give any clue as to the ultimate goals of the cult.
A sect is made up of multiple warbands, called thrallbands within the Legion, which can also act independently of each other. With several units of Thousand Sons bolstered by auxiliary troops and vehicles, a single thrallband can obliterate an enemy fortress or turn a city into a blazing pyre. A number of thrallbands operate in complete isolation -- some have been exiled from the Planet of the Sorcerers, while others chose to leave to pursue their own ends. But even these forces ultimately serve the goals of one of the nine Thousand Sons cults, whether they themselves know it or not.
The Athanaean Cult's members were practiced masters of the discipline of telepathy, and were able to transmit their thoughts and read the thoughts of others. They often acted as the Legion's communications officers since their communications were secure from all but other psykers and they assisted the Corvidae in conducting intelligence operations based on psychically-gleaned knowledge.
While the Corvidae could provide an overall strategic direction based on their reading of the likely probabilities of future events occurring, the Athanaeans could use their ability to read the minds of the enemy to shape the Legion's battlefield tactics more directly, through weapon choice, the types of troops to be deployed and where, and the choice of the most advantageous terrain.
The Corvidae were skilled in the psychic discipline of precognition, determining the likely probabilities of future events. They served as the XV Legion's seers, warning their Battle-Brothers of dangers before they materialised. The Corvidae Cult also helped guide the Thousand Sons Legion along the lines of Fate during times of conflict and in pursuit of their overall psychic and material growth as a Legion. The Corvidae were responsible for much of the Legion's strategic planning.
Corvidae could determine events that were not only far in the future but were immediately about to happen, which allowed them, for example, to navigate a minefield before it exploded or to know the exact sequence in which a series of enemy soldiers would fire at a particular target. The Cult badge of the Corvidae was a black raven's head.
The Pavoni Cult tended to be the most egocentric of the known Cults within the Thousand Sons Legion, as they had developed the psychic discipline known as physiokinesis. Physiokinesis allowed the Pavoni to manipulate body chemistry and physiology within themselves as well as others, a very useful trait for a group of already superhuman warriors. Skilled practitioners of physiokinesis were able to alter their physical appearance by manipulating the physical characteristics of their facial features at will as well as making themselves immune to the harmful effects of dehydration and other physical ailments.
On the field of battle, the Pavoni were able to generate lightning by unleashing the inherent bioelectricity of their own nervous systems and focus it offensively, as well as cause the hearts of enemy warriors to explode by literally boiling the blood within their veins. When using these abilities against their foes, the Pavoni had a reputation for venality and spite which bordered on the sickening. The Pavoni were also the designated healers of the Legion, as they were capable of accelerating cellular growth and protein synthesis, which made them extraordinary medics who saved the lives of countless Astartes when even the Apothecaries could not.
The Pyrae were pyrokinetics, meaning that they had developed the ability to both generate and control fire, the power for which was drawn from the Warp. The Pyrae could both generate lethal bursts of fire from their bodies that they could shape into a number of different forms, including projectiles fired from their hands as well as fire shields that could hold back foes and melt away incoming weapons fire. The Pyrae could manipulate existing or standing sources of fire and with their connection to the Warp could lower the temperature of flames striking their own bodies or the bodies of others, effectively making them immune to the effects of fire or great heat. The Pyrae also developed secondary psychic abilities that allowed them to control and manipulate mechanical automata like the robots of the Legio Cybernetica and even the massive Titans of the Collegia Titanica.
These secondary abilities were known as technopathy. At the time of the closing years of the Great Crusade, the Pyrae Cult was in the ascendence within the XV Legion's hierarchy, while the Corvidae Cult was at its lowest ebb for nearly fifty standard years. For centuries, the Corvidae had been pre-eminent within the ranks of the Thousand Sons, but in the Legion's final decades within the Imperium, their power to read the twisting paths of the future had diminished until their seers could barely penetrate the shallows of things to come. The Cult badge of the Pyrae was a phoenix wreathed in flames.
The members of the Raptora Cult were gifted practitioners of the psychic discipline called telekinesis, and were known as telekines. In battle, a Raptora Cult member could psychically fling physical objects at their enemies or rip their enemies bodies' apart through the application of immense telekinetic power drawn from the Immaterium. When used defensively, telekines could generate barriers of invisible kinetic force known as "Kine-Shields" to block physical attacks on themselves or others.
During the Burning of Prospero, the massed members of the Raptora Cult generated a massive kine shield over the whole of the city of Tizca intended to protect it from an orbital assault by the Space Wolves. The shield eventually failed when the sheer power unleashed by the Loyalists' assault upon the kine-shield proved to be more than the individual Raptora Astartes could mentally bear. They fell exhausted to the terrible mental strain, one by one, until the psionic shield collapsed.
Cult of Change
The Cult of Change is anathema to order. They are the great unravellers, launching their armies wherever civilisation and reason exist. Similarly, in places of utter anarchy, the cult appears to impose their ever-shifting will.
Cult of Duplicity
The Cult of Duplicity is unique within the Legion in that it both is and is not guided by a unified desire. The Sorcerers of this cult are by their very nature deceivers, at once appearing fractured and singular in their purpose. As such, it is impossible to know whether the sects within the cult are acting independently or as part of a singular, terrifying plan.
Cult of Knowledge
The Cult of Knowledge is also drawn to the many curios hidden throughout the galaxy, particularly tomes of eldritch learnings, dark secrets and paradoxical logics. Through such lore, the cult is able to extrapolate the weaknesses in their enemies, and in the fabric of reality itself.
Cult of Magic
The Cult of Magic is dedicated to the pure and unfettered use of sorcery. Their bloody campaigns are launched to secure arcane objects held by Imperial, xenos and other Chaos forces. These artefacts are then used as foci in the weaving of devastating spells.
Cult of Manipulation
The Cult of Manipulation is similarly deceptive, using its tendrillar web of influence to sway the actions of its enemies. Vast networks of mortal and daemonic spies allow the cult to oversee their plots as they unfold through assassination, possession and the wreaking of pure havoc.
Cult of Mutation
The Cult of Mutation embodies the transfiguring aspect of Tzeentch. Not only do they embrace the warping of flesh, but also the warping of reality itself. By their hand civilised planets are transformed into Daemon Worlds, and entire populations moulded into grotesque abominations.
Cult of Prophecy
The Cult of Prophecy is guided by incessant whispers that bleed from the Warp. From these they divine the outcomes of multiple futures, and seek out events that can be twisted to their own purpose.
Cult of Scheming
The Cult of Scheming is perhaps the most insidious of the cults, for the creation of convoluted plots is to them a form of profane worship. Every conquest and withdrawal is a perfectly planned manoeuvre, a single step that leads towards some unseen master stroke.
Cult of Time
The Cult of Time is similarly enthralled by the future, as well as the present and past. They view the flow of time as an unwrought resource that can be shaped into a weapon. By their victories, ripples are sent both forwards and backwards in time, so that their enemies may be defeated before they are even engaged.