Brotherhood of the Phoenix

The Brotherhood of the Phoenix was a warrior lodge within the Emperor's Children Legion during the Great Crusade and Horus Heresy eras. This confraternity of warriors was instituted after the III Legion had spent some time fighting alongside their brother Legion, the Luna Wolves, although given the Emperor's Children's love of formal hierarchy, the Brotherhood of the Phoenix was much more formal in structure and behaviour than their brethren Legions' warrior lodges and was open for membership only to their Primarch Fulgrim, the Lord Commanders, and the company Captains to maintain the Legion's strict leadership structure. The Brotherhood of the Phoenix would eventually be used as the conduit by which Fulgrim and the other members of the Emperor's Children who were corrupted by Slaanesh would seize control of the Legion and rid themselves of Imperial Loyalist elements during the Istvaan III Atrocity.

History
During the early years of the Emperor's Great Crusade to reconquer the galaxy and reunite the disparate worlds of humanity, there was one great disaster that would leave the greatest mark upon the early decades of the III Legion's existence. This was the catastrophic loss of nearly the entire gene-seed stock of the Emperor's Children. Coming within a solar year of their great moment of triumph fighting at the Emperor's side at Proxima, it was to prove a turning point that was to forever alter the III Legion's future. When Fulgrim was finally found and reunited with the III Legion, the Astartes Legion that shared his genetic inheritance, he found not a resplendent host as did so many of his brothers, but a mere 200 Battle-Brothers. Thus, it was necessary that Fulgrim and his warriors be integrated into the ranks of another Legion until such time as their numbers were sufficiently restored for them to take to battle on their own. The Legion to which Fulgrim and his warriors were assigned was the XVI Legion, the Luna Wolves, the Legion of Horus, the most favoured son and preeminent warrior of all the Primarchs.

When the Emperor’s Children had fought alongside the Luna Wolves early after the rediscovery of their Primarch Fulgrim, they had formed great bonds of friendship with the warriors of Horus, and in the times between the fighting, a few loose tongues amonst the warriors of the XVI Legion had spoken to their brothers in the III Legion of the existence of their Warrior Lodge. The Luna Wolves' lodge was, in theory, open to any warrior who desired to be a member, an informal place of lively debate where rank held no sway and a man could speak his mind freely without fear of reprisals. Eventually a few Astartes from the Emperor's Children were permitted to attend one such meeting, a pleasant evening of honourable camaraderie under the titular leadership of the Lodge Master Serghar Targost. Some enjoyed the meeting, despite the clandestine nature and theatrics of it, but some remained uncomfortable with the informality and mingling of the ranks. In the traditionally hierarchical Emperor’s Children Legion, only warriors of officer rank could join their similar confraternity which was soon created within the III Legion.

Eventually, over the course of several decades, the Emperor's Children's ranks were swelled by new Astartes who had been recruited from both Terra and Fulgrim's homeworld of Chemos, where the Legion had established its fortress-monastery at the old factory fortress of Callax. When the Emperor's Children were judged to have reached an appropriate size, Fulgrim was given command of the 28th Expeditionary Fleet of the Great Crusade and set off on his own course of conquest, returning dozens of human-settled worlds to the rule of the Emperor. Among them was the advanced xenos world of Laeran, where Fulgrim's fate would be sealed.

Fulgrim's Fall
The point at which Fulgrim and the Emperor's Children embraced darkness is not known. Some amongst those who serve the Emperor pointed to Fulgrim's cleansing of the dangerous xenos known as the Laer as the event that finally doomed him, as there are indications that the malign Forces of Chaos used this event to ensnare Fulgrim and begin the rapid corruption of the Emperor's Children. It is believed that Fulgrim first fell from the Emperor's grace on the xenos planet called Laeran, officially designated as Twenty-Eight-Three, being the third world the 28th Expedition had brought to Imperial Compliance. Unbeknownst to the III Legion, the serpentine Laer species were corrupted xenos worshippers of the Chaos God of Pleasure, Slaanesh. Though the resource-rich Ocean World of Laeran would be of immeasurable value to the Crusade of the Emperor, its alien inhabitants did not wish to share what blind fortune had blessed them with. They had refused to see the manifest destiny that guided Mankind through the stars and had made it abundantly clear that they held the Imperium in nothing but contempt. The III Legion's diplomatic advance had been rebuffed with violence, and honour demanded that they answer in kind.

Fulgrim's 28th Expeditionary Fleet of the Great Crusade conquered Laeran for the Imperium, exterminating its hostile native reptilian species. Completely unaware of the real dangers he and his Astartes Legion faced on the Chaos-corrupted world, Fulgrim ordered the Emperor's Children and the other forces of the 28th Expeditionary Fleet to assault the planet and conquer it for the Imperium within a single Terran month, completely eradicating the Laer species in the process. During the final slaughter of that serpentine xenos race, Fulgrim and his Astartes discovered the great temple dedicated to Slaanesh that lay on the central floating coral island of Laeran. The Imperium, ignorant of the existence of the Chaos Powers at this time and holding to the extreme rationalism and atheism of the Imperial Truth, did not realise the significance of such a find or what they had really discovered. The expedition led by Fulgrim began to be unwittingly corrupted by the temple's potent and malign influence. After defeating the temple's fanatical Laer defenders, Fulgrim discovered what the Laer were so fiercely protecting -- at the centre of the chamber of the unholy temple was a circular block of veined black stone, and embedded within was a tall silver sword with a gently-curved blade and a crude amethyst gem set in the pommel. This sword was not only a potent Slaaneshi artefact but also the physical vessel of a Greater Daemon of Slaanesh.

Once Fulgrim had claimed the blade as his own, the daemon within it began whispering in his mind and corrupting his soul towards the service of Slaanesh. Thinking the whispers in his mind was only his own subconscious speaking to him, Fulgrim began listening to what it offered. Eventually, he discovered these were actually the whispers of the daemon that existed within the blade. After a lot of persuasion from his brother Horus, himself already corrupted by the Ruinous Powers after his injury on the moon of Davin, Fulgrim gave himself over to Chaos, and found his particular patron in the Prince of Pleasure, who offered the Primarch a route to the ultimate perfection he so craved for himself and his Astartes, free of all morality and dependent upon the pursuit of ultimate self-obsession. Many of the Legion's senior commanders that were with their Primarch during the final assault on the Laer temple were similarly enraptured by the dazzling sights and strange discordant music as the cacophonous flood of sensations assaulted them with surges of light and noise. After their return to the fleet in orbit, many of these affected Astartes continuously sought ways to stimulate their senses in an effort to recapture what they had felt in the Laer temple, both on and off the battlefield. As their Primarch fell to the whispered temptations of the Daemon-possessed sword he had taken from the Laer temple, the Emperor's Children Legion continued its descent into a downward spiral of corruption marked by the corrupted Astartes' insatiable desires to satisfy their hedonistic wants.

Istvaan III Atrocity
Before Horus openly launched his rebellion to overthrow the Emperor, an opportunity presented itself that would enable him to get rid of the Loyalist elements within the Astartes Legions under his command. The Imperial Planetary Governor of Istvaan III, Vardus Praal, had been corrupted by the Chaos God Slaanesh whose cultists had long been active on the world even before it had been conquered by the Imperium. Praal had declared his independence from the Imperium, and had begun to practice forbidden Slaaneshi sorcery, so the Council of Terra charged Horus with the retaking of that world. This order merely furthered Horus' plan to overthrow the Emperor. Although the four Legions under his direct command -- the Sons of Horus, World Eaters, Death Guard and the Emperor's Children -- had already turned Traitor and pledged themselves to Chaos, there were still some Loyalist elements within each of these Legions that comprised approximately one-third of their forces. The corrupted Fulgrim and his senior officers within the Brotherhood of the Phoenix secretly convened in order to mark those for death that were judged to be fractious or deemed disloyal to their Primarch and the Warmaster.

Horus, under the guise of putting down the rebellion against Imperial Compliance on the world of Istvaan III, amassed his troops in the Istvaan System. Horus had a plan by which he would destroy all of the remaining Loyalist elements of the Legions under his command. After a lengthy bombardment of Istvaan III, Horus despatched all of the known Loyalist Astartes down to the planet, under the pretence of bringing it back into the Imperial fold. At the moment of victory and the capture of the Choral City, the planetary capital of Istvaan III, these Astartes were betrayed when a cascade of terrible Life-Eater virus-bombs fell onto the world, launched by the Warmaster's orbiting fleet. Even before the first treacherous blow was struck, Horus' grand plan had, unknown to him, begun to unravel. Before the virus-bombs fell, the impending atrocity had been discovered by several Astartes among the orbiting fleet who remained loyal to their Emperor and their comrades and who resisted.

The Loyalist Captain Saul Tarvitz of the Emperor's Children had the discovered the far-reaching treachery of the Warmaster and stole a Thunderhawk gunship and was able to reach the surface of Istvaan III despite pursuit, bringing a timely warning to those Loyalist Space Marines he could find of all four Legions of their impending doom. Those that heard or passed on Tarvitz's warning took shelter before the virus-bombs struck. The surviving Loyalists, under the command of Captains Tarvitz, Garviel Loken and Tarik Torgaddon, another Loyalist member of the Sons of Horus, fought bravely against their own traitorous brethren. The few remaining Loyalists of the Emperor's Children Legion fought bravely on Istvaan III, led by Captains Saul Tarvitz and Solomon Demeter. To prove his worth and loyalty to Lord Commander Eidolon of the Emperor's Children -- and thus to his Primarch, Fulgrim -- Captain Lucius of the 13th Company of the Emperor's Children, the future Champion of Slaanesh known as Lucius the Eternal, turned against the Loyalists that he had fought beside because of his prior friendship with Saul Tarvitz. He wanted to punish Tarvitz for taking command of the defence, which had incited Lucius's fierce jealousy of his fellow captain. Lucius slew many of his former comrades personally, an act for which he was then accepted back into the III Legion on the side of the Traitors. In the end, the Loyalists retreated to their last bastion of defence, only a few hundred of their number remaining. Finally, tired of the conflict, Horus ordered his men to withdraw, and then had the remains of the Choral City bombarded into dust for a final time from orbit.

Fulgrim's Fate
Those that served in the III Legion had no idea that their beloved leader was clawing ineffectually at the bondage of his own mind in which he was held. Only the swordsman,Captain Lucius of the 13th Company, had appeared to realise that something was amiss with Fulgrim, but even he had said nothing. Lucius came to the conclusion that somehow that the entity that paraded around as their Legion's lord was an imposter. Determined to free his Primarch by any means at his disposal, Lucius secretly convened the Brotherhood of the Phoenix. This had to be done with the utmost secrecy, for by this time the corrupted senior officers had become powerful, volatile and self-obssessed with the pursuit of their individual pleasures. Also, many of these senior officers carried a loathing for Lucius, whom they viewed as a despised upstart. Through his skilled oratory, the swordsman was able to persuade his mercurial brothers that the Primarch was not himself. He further challenged their egos and stroked their vanity, tempting them into boldly capturing their Primarch. Shortly after, the Brotherhood of the Phoenix ambushed the Primarch, and despite taking several casualties, manage to subdue their lord by rendering him unconscious.

During a torture session carried out under the direction of the III Legion's Chief Apothecary Fabius, Lucius suddenly realised that they had been misled. Misinterpreting the situation, they had been duped by their lord. Lucius immediately bended his knee and prostrated himself before his Primarch as Fulgrim easily tore himself free from his restraints. His fellow conspirators all bowed to their lord and master. Content that his favoured sons had learned from the experience, the Primarch did not punish them for their transgressions, for he was not the daemon-possessed shell of the Phoenix as he had allowed his Astartes to believe, but the man himself. Following these events and those that would follow over the next seven years as the Horus Heresy played out to its inevitable conclusion, it is not known if the Brotherhood of the Phoenix still exists within the hierarchy of the corrupted Emperor's Children Traitor Legion.