Sector: The Praeses Vahlandia

The Praeses Vahlandia is the name of a now-defunct Oath of Defense between four Chapters of the Adeptus Astartes, who's Homeworlds are (were) present within the Vahland Sector. Using the Cadian Gate's "Astartes Praeses" as a model, there were high hopes that attempting to use similar models on the Sector/Sub-Sector level would be a boon to Imperial control, and would significantly improve military response times, as well as go a long way to curtail potential insurrection and piracy. It is likely though that regardless of its eventual result, adoption of similar cooperatives would have been rare at best throughout the wider Imperium or even on the Eastern Fringe. Vahland Sector has long been influenced by progressives and moderates in the Administratum and Militarum, due mostly to its close proximity to Ultramar, and the sometimes willfully independent nature of Sectors on the Rim of Imperial space, this alongside the generally affable relationships of the local Astartes chapters made the Praeses Vahlandia experiment a viable option. 

Created only a short two centuries before the Breaking of the Cadian Gate and the onset of the Cicatrix Maledictum, the Praeses Vahlandia was born to much pomp and circumstance, during the Triumph of Sanhorn, following the successful eradication of the xenos Septimanian Empire. It was comprised of the Imperial Dragoons, Centurions of Innocence,  Hammers of Ornus, and Radiant Blades' Chapters. Of these only, the Imperial Dragoon's would remain in the Emperor's Surface by the time of the Indomitus Crusade and the Primarch Guilliman's return, with the others missing, dead, or become slaves to darkness. 

For the short period of their operation, before the beginning of the Noctis Aeterna, the Chapters of the Praeses Vahlandia, were able to coordinate on a number of different fronts, suppressing the spread of lesser alien species along the frontier, destroying reaving warbands of traitors, and aiding in the destruction of insurrectionist elements. When the call to defend Cadia came, less illustrious Chapter's on the extreme edge of the Imperium were tasked with holding the territories together as men and material were redeployed to halt the Black Legion and their allies at the gate. The shock and confusion that descended on the Imperium in the aftermath of the 13th Black Crusade's attack, is well known and the scope of the calamity is still far from comprehensively understood. In Vahland Sector, the Noctis Aeterna, was typified by raging warp storms, major actions by Insurrectionists, and Heretic Cults the Sector over, and not least of all predatory attacks of opportunity by bordering aliens. With inter-sector communication non-existent, and in sector astro telepathy not much better, Imperial forces moved to bulwark what systems they could. 

The Imperial Dragoons withdrew to their Chapter's Homeworld, where they reinforced an already formidable joint Astartes and Knight holding into a stellar fortress, a system of six worlds, defended by 25 million Knightly Armsmen and Defense Force Militia, 2/3rds of House Trask, and 845 Astartes of the Imperial Dragoons, as well as their associated Navy Assets and the Chapter Novitiates who were organized into rapid reaction units.  The entire system was cut-off four months into the preparatory work by Warp Storms, which did not abate for almost a century. When the Indomitus Crusade arrived, the systems fourth world had partially turned into a mass of eyes and undulating flesh, apparently, the Chapter's Librarium had been directly responsible for halting this process in what they only refer to as The Twelfth Sight Conjuction, which they stubbornly refused to provide any details on. The Armsmen and Militia had been nearly annihilated by unceasing decades of attack by daemonic hordes, and the Chapter now numbers barely over three hundred non-primaris brothers. It was the most fortunate of the Praeses Vahlandia 

The Hammers of Ornus joined with Battlefleet Vahland, and defended the Sector Capital world of Hiser Marina, from an armada of Word Bearers and Kytixi (a chaos tainted faction within a local xenos species) The Chapter spent its resources in the orbital war, allowing portions of Battlefleet Vahland to withdraw from the fighting once the battle turned against the Imperium. The last of its Battle Brothers are thought to have been slain in glory aboard its last surviving vessel Ender of Recalcitrance, the 4th Companies Battle Barge, as it dueled with several Word Bearer vessels before being obscured by the blast wake of a dying Kytixi ship.  During the Liberation of Hiser Marina by the Indomitus Crusade, the remains of several of the Chapter's vessels, and the desecrated bodies of only 14 of its Brothers were recovered. The vessels were destroyed and cleansed with flame, by order of Robute Guilliman for fear of the taint of Chaos. A continent on Hiser Marina is now named Ornus in the chapter's honor, their little remaining war gear was given to the Imperial Dragoons who were in attendance at the Liberation. There are currently no plans to refound the Chapter.

The Centurions of Innocence attempted to safeguard refugees fleeing from poorly defended outer worlds, as the forces of Chaos began pouring into the Sector. Prevailing moods in the Ecclesiarchy and Inquisition tended to feel it was much safer, to simply annihilate these refugees columns than allow a possible vector for internal corruption. This went against the sensibilities of the Salamander's descended Chapter, who shepherded millions into their Homeworld,  The Sink of Erasmus, even going so far as to engage in a skirmish with members of the Adepta Soritas over the issue on one occasion. Puritanical members of the Ordos Vahland, took this as a sign of the Chapter's straying from the path, that they would engage in internecine conflict when the galaxy was in such turmoil.  The Centurions gathered their allies together to safeguard their Homeworld and nearby Forge Worlds, hoping to secure as much manufacturing infrastructure and as many citizens as possible during the Crisis. It is not well understood what happened next, because of the chaos that was to follow, but it is believed that the Chapter suffered an ideological split, and fractured. With a portion of the Centurions skewing the Chapter's version of the Promethean Cult, into the worship of Brass Drake icons, minor bloodletting and obsessing over martial pride and improving their ability to protect their domain at any cost. A force, seeing the signs, attempted to stamp out the signs of Corruption in their ranks, but failed and were ultimately ousted from the Sink of Erasmus.  This group of loyalists fought as Gurriellas in the Sector for years, until the Indomitus Crusade arrived, these former Centurions of Innocence were apprehended and sentenced to death for their brethren's crimes. The Sink of Erasmus, has never been liberated, due to the outbreak of the Plague War in Ultramar, and the Pilgrims of Rust's Insurrection in Vahland. 

The Radiant Blades are the greatest enigma in the sector, as they moved to hold the Shrine World of Vahl, the holiest site in the Sector. As darkness fell and the other Chapters of the Praeses Vahlandia fought against the madness, something occurred on Vahl, members of the Inquisition believe that the entire planet was taken entire into the warp, though the Ecclesiarchy and the Adeptus Astra Telepathica suggest this is unlikely because of the sites spiritual significance. There are Rouge Traders who claim to have heard from alien merchants beyond the fringe of the Imperium that the world rests now in the Interstellar void, emitting powerful radiation and orbited by a roughly equally sized stellar body, made of an unknown material, the blackest of black in color. It is unknown what occurred precisely, but investigations are still ongoing.  When the Indomitus Crusade arrived at the location of the Vahl system, the planet was simply gone, no warp taint could be detected, no debris indicating an orbital battle was found. The only clue was the detached Sarcophagus of Brother Ancient Calena, the venerable ancient unfortunately had died in the void, he had lashed to his case with bolter straps, a single cache of viable gene seed, which it seems he sacrificed his power reserves to keep at a stable temperature. His entire combat log had been deleted and replaced with a single line of code reading 

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The Praeses Vahlandia fell in glory, mystery, and ignominy, and with their actions have shaped the Vahland Sector for thousands of years to come.