Signus Prime - History: For untold generations, the Signus Cluster had been a centre for Human civilisation. Great hive cities littered the seven worlds of the Cluster and huge industrial complexes burrowed into the fifteen moons. But amongst the uncounted millions settled within the Signus Cluster lurked sinister Chaos Cultists.After his own corruption, Horus had set many plans into motion to prepare for his rebellion against the Emperor of Mankind. One of these had been to send agents to Signus Prime, the capital world of the Signus Cluster, from Davin and other worlds with a strong Chaos presence.At the onset of the Horus Heresy, Warmaster Horus sent a messenger aboard the Word Bearers vessel Dark Page to a mustering of the Blood Angels Legion, informing Primarch Sanguinius that the worlds of the Signus Cluster had gone dark, with no further communications with the wider Imperium due to the reemergence of a hostile xenos species called the Nephilim, thought to have been destroyed by the Blood Angels, Luna Wolves and White Scars Legions during the Great Crusade.Horus called for the Blood Angels to respond in force to the return of this threat, and Sanguinius agreed, not yet aware of his brother's treachery, and mustered the bulk of his Legion along with the Word Bearers on the Dark Page and an unexpected contingent of Space Wolves that had joined the Blood Angels fleet on the express command of Malcador the Sigillite, the Regent of Terra to ensure that Sanguinius remained loyal to the Emperor.In the system itself, there had been an outbreak of unexplained phenomena over the course of several solar months. The worlds of the system were suffering from a massive increase in birth defects and mutations, inexplicable meteorological patterns and the mysterious deaths of the astropaths assigned to the Imperial colonies of the cluster. The colonists had called for help, appealing to the Administratum, the Imperial Army and even the Legiones Astartes for aid. Eventually, help appeared to arrive in the form of a man named Bruja, an emissary of Horus, whose betrayal of the Emperor still remained secret at this time. Bruja was in truth an agent of the Chaos Gods, a native Davinite and a priest of the Temple of the Serpent Lodge that had corrupted the Warmaster to the service of the Ruinous Powers. Soon after his arrival in the system, the priest's possessed form burst apart and allowed the Slaaneshi Keeper of Secrets Kyriss the Perverse to enter the Materium in the Signus Cluster.Within solar months, Kyriss and the agents he soon suborned infested the rabble of the Signus Cluster and in their teeming numbers hid the witch-cabals that later summoned Daemons to Signus. When these agents and Chaos Cultists received a signal from Horus not long before the Isstvan III Atrocity in 005.M31, they rose up in a violent insurrection and seized power within the Signus Cluster, summoning Daemons into realspace to lead them and rule over the star system.Daemons soon stalked the hive cities and established foul palaces across the entire star system. The Human population of the Signus Cluster was enslaved, reduced to fodder for the minions of Chaos. Powerful summoning spells cast by the witch-cabals allowed the Daemons free reign over Signus. In addition to this, thousands of Signan psykers had been possessed by Warp entities and become Daemonhosts.The Signus Cluster had become a veritable extension of the Realm of Chaos within the Warp in only a short time, and a demesne of Daemons. Kyriss the Perverse, a Keeper of Secrets and one of the Greater Daemons of the Pleasure God Slaanesh, now ruled the Signus Cluster. Once the cluster's primary world was under the control of Chaos, Kyriss raised for itself a great palace on Signus Prime that it named the Cathedral of the Mark. This blasphenous edifice was crafted from the bones of every man, woman and child murdered by the servants of Chaos on Signus Prime.Then the Daemonic legions under Kyriss' control swept from Signus Prime across the rest of the system, destroying the work of millenniums of Human civilisation and eradicating the populations of whole worlds. Almost the entire population of the Signus Cluster was enslaved, corrupted to the service of Chaos or just butchered outright, and hope fled from those few who survived.The 7 worlds and 15 moons of the trinary system were soon in thrall to this mighty Daemon lord and its teeming hordes. The Daemons were aided by the machinations of the Chaos Cultists. These bands of madmen opened their worlds to the creatures of the Warp, conjuring powerful summoning spells and offering themselves up for possession.The rest of the Human population of Signus Cluster had been annihilated or enslaved, their only fate to be consumed by the horrors of the Warp. The entire star system became a charnel house, a place of evil and a home for the creatures of the Immaterium. There was never so base a betrayal as this one, for Sanguinius looked to Horus as a brother, and never would have believed he, his Legion and literally billions of people would be sacrificed to the foul denizens of the Warp.Their deliverance came in the form of the Primarch Sanguinius and his entire Blood Angels Legion, who came to the Signus Cluster on a mission from the Warmaster Horus to supposedly cleanse it of domination by a xenos species known as the Nephilim. In truth, Horus had sent the Blood Angels to the Daemon-infested star system to see them either destroyed or corrupted to his cause.In the wake of the Blood Angels' unexpected but difficult victory over both Kyriss and the forces of the Bloodthirster Ka'Bandha in the resulting Signus Campaign, the cluster was cleared of all Daemonic infestation. A tactical Cyclonic warhead was deployed to destroy the blasphemous Cathedral of the Mark and much of the continent that surrounded it.Signus Prime and the entire Signus Cluster were thereafter quarantined from the rest of the Imperium and declared mortae perpetua ("forever dead"), forever off-limits to any Human interaction through the use of special warning beacons placed all around the system's circumference. The Blood Angels also expunged all of their own records of their presence on Signus Prime to prevent the spread of Chaos corruption, and resettled what few uncorrupted survivors they had encountered on new homes in neighbouring star systems.