Changes

[[Imagefile:1KSonssquad.jpg|thumb|right|200px|The Thousand Sons on crusade{{Fn|71a}}]]With this stabilisation of the gene-seed, the Fifteenth Legion got its second chance. Recruiting from Prospero, they were able to rebuild their numbers – though they would never become numerous – and return to the Great Crusade, this time led by their primarch.

While little is known about how the Thousand Sons were organised before the coming of Magnus, it is recorded that they were not considered particularly different from a typical Legiones Astartes apart from their psychic abilities (which resulted in the legion possessing the most powerful [[Librarianslibrarians]] of the era{{Fn|1a}}). When Magnus took command, his directions (influenced by his development on Prospero, as well as Prosperine culture itself) would cause some organisational and hierarchical changes within the legion. [[Chapters]] were referred to as '''Fellowships''' within the Thousand Sons, of which there were a maximum of 10. However, at the conclusion of [[Kamenka Troika|one particularly bloody campaign]], the Thousand Sons had lost almost 900 Astartes, effectively wiping out an entire Fellowshipfellowship. Rather than rebuild it, Magnus decided to reorganise and maintain the legion as one of 9 Fellowships, an organisation he referred to as the '''Pesedjet'''. Two special units were created within the legion; , the elite [[Scarab Occult]] [[Terminators]] and the [[Hidden Ones]] of the [[Scouts|Scout Auxillia]]. The legion's command structure was adapted to include Prosperine philosphy in the form of the '''Rehati''' (the coven of Magnus), a second command-track in which the legion's senior officers were ranked according to psychic ability and influence.{{Fn|3b}}

The resurgent Thousand Sons brought their fair share of worlds into compliance with the Imperium of Man, and as such their main method of victory (diplomatic guile and trickery) was not questioned by the body Imperialimperial. However, as the Crusade entered wilder regions of space, more and more hostile forces were encountered that deployed powers similar to those that the psychic warriors of the Thousand Sons wielded. This event, along with the ever-present rumours of 'witchcraft' and 'sorcery' surrounding the legion, resulted in [[Mortarion ]] once more raising his voice in condemnation of the Thousand Sons.{{Fn|1a}} This time he was joined by [[Leman Russ (primarch)|Leman Russ]], whose long-held distrust of the legion came to a head after he witnessed the return of the flesh-change in the Thousand Sons during a joint action on the world of [[Shrike (planet)|Shrike]].{{Fn|3c}} It was decided that Magnus and his legion would be called to account, and the whole matter of Astartes astartes employing psychic powers at all would be ruled upon. This event was known as the [[Council of Nikea]], and at it – after much deliberation – the Emperor announced that no Astartes astartes must ever again employ the use of psychic powers, upon pain of destruction visited upon them by the Emperor himself.{{Fn|3d}}

Stunned, the Thousand Sons effectively withdrew from the Crusade, returning to Prospero. It was during the period that followed that Magnus discerned the approach of the [[Horus Heresy]] and employed both his own powers and that of his senior legionaries to try to save [[Horus|his brother's]] soul. Failing, he once again marshalled the powers available to him and attempted to psychically warn the Emperor of his favourite son's betrayal. News of this a sanction fleet, meanwhile, had previously reached the ears of the now-corrupted [[Horus]] himself. Sensing an opportunity, the [[Warmaster]] contacted [[Leman Russ]], commander of the fleet, during the trip to Prospero. Speaking with his brother, he was able to convince him that "to return Magnus to Terra would be a waste of time and effort", in direct contradiction of his orders. Horus confirmed to his traitorous council of war that he believed this interjection of his into the Emperor's own decree would result in Magnus never leaving Prospero alive.{{Fn|31}} This action, which went so catastrophically wrong, would doom the Thousand Sons , as, in accord with the Judgement Judgment of Nikea, the Emperor visited destruction upon Magnus and the Thousand Sons in the form of [[Leman Russ ]] and his [[Space Wolves]].{{Fn|1}}

Magnus had realised his grave mistake in warning the Emperor in the method he chose, and had also been confronted with the stark reality that he was not as in control of the [[warp]] or his powers as he thought. Additionally, a [[Tzeentch|power of the warp]] had spoken to him, revealing to him that Magnus had been its pawn since the time it had helped him save his legion from the flesh-change...and perhaps even long before that. [[Imagefile:1KSonburning.jpg|thumb|right|200px|The Burning of Prospero{{Fn|71b}}]] Distraught, Magnus resolved to accept whatever punishment the Emperor saw fit. Thus, to prevent his legion from defending Prospero , he dispersed the Thousand Sons fleet from orbit, shut down the orbital defences , and wrapped his homeworld in a 'psychic cocoon' which prevented anyone from communicating or using their powers beyond its boundaries. Thus , the Space Wolves managed to attack Prospero completely by surprise. The Thousand Sons legionaires themselves, however, did not share Magnus' s acceptance of defeat and punishment, and so took up arms against the invaders. The Thousand Sons managed to hold [[Tizca]] (the only surviving city on the planet) for a period of time before they were eventually pushed back, the assault of the Space Wolves , led by their primarch, as well as forces from the [[Sisters of Silence]] and the [[Adeptus Custodes]] , proving too much. Magnus eventually joined the battle when it appeared that the final moment of extermination for his legion had arrived. [[Leman Russ |Russ]] engaged [[Magnus ]] in a devastating duel in which the [[Leman Russ|Russ ]] was ultimately victorious. In response , [[Magnus ]] finally, consciously gave in to [[Tzeentch|the daemonic voice]] that had been tempting him and invoked ancient sorceries in order to escape Prospero with the remnants of his legion. In the [[Eye of Terror]], a [[Daemon World]] had been prepared for them by [[Tzeentch|their new patron]].{{Fn|3e}}