A normally quiet and productive system spinward of the Markayn Marches, Gelmiro’s main tithe planets (Gelmiro Primus, Gelmiro Secundus and Gelmiro Tertius) are now desolate wastelands, the home of abominable mutations and crazed zealots. In 738.M41, an uprising that engulfed the Calixis Sector unlike any conflict since the Angevin Crusade emerged that came to be known as the "War of Brass."
The Gelmiro Cluster and its hive worlds fell into sedition following the charismatic leadership of the insane cleric Anolian Hesh, calling himself the "Emperor of Brass," debasing themselves into the worship of the Ruinous Powers. Loyal to the Emperor of Brass, frenzied fanatics from the wealthy and powerful worlds of the Gelmiro Cluster murdered every functionary of the Adeptus Administratum, ritually desecrating the bodies of the fallen. Significant portions of the affected planetary populations accompanied their new overlords into treachery beyond redemption.
His heretical followers ignited stolen atomics on the three worlds, destroying nearly all of the system’s key military assets. Dissatisfied with holding the powerful worlds of the Gelmiro Cluster in his augmented fist, the Emperor of Brass and his renegades sponsored heavily militarized and bloody, the renegades quickly sponsored and armed rebel groups on worlds throughout several nearby worlds. Soon after, a full-scale rebellion threatened the wider Calixis Sector. The death toll continued to rise as he publicly tortured and executed loyal Imperial servants and citizens. The Sector Governor was forced to call upon all available forces to stem the bloody tide. From across the Calixis Sector and beyond, loyal units converged upon the Gelmiro Cluster. Investigating forces were greeted with attacks from planetary defenses and traitor naval ships, and it was only after intense orbital battles that land forces could be deployed. When counter-attacked, these groups revealed the hand of dark forces drawn from the Eye of Terror in their number.
These Imperial forces first pushed through the neighboring regions, and crushed the nascent rebellions there with heartless efficiency. Amongst these forces that rose to answer the Governor’s call were several battle Titans of the Legio Venator, and an entire Explorator fleet with support from the mysterious Ordo Reductor.
Crusader Welgon Rouss became a hero amongst the Inquisitorial personnel attached to the endeavor for his actions on the world of Gelmiro Tertius during the War of Brass. When the daemonic forces of the enemy attacked the gates of Sub-Hive Mortia–5, Rouss stood alone against their onslaught. Though the main gates were wrought asunder, the breach was only wide enough for three men to stand abreast, and this was where Rouss made his stand. With suppression shield and blessed power sword, he held back the daemonic incursion for four hours, until the forces of Daemonhunter Markus Eddards-Konnor launched a drop-pod assault into the heart of the malefic beings and scattered them to the winds. Rouss would go on to lead the bodyguards of no less than four Lords of the Calixian Conclave. This conflict is also responsible for the birth of the Radical Inquisitorial Faction known as the Oblationists.
The campaign against the Emperor of Brass and his burgeoning rebellion, known as the War of Brass, lasted just over three years, but even in that short time the fighting proved especially vicious. In the end, several companies of Space Marines were needed to reduce the final hives to rubble. In the final, desperate battles at the heart of the Gelmiro Cluster, several records were discovered hinting that support and reinforcement had been supplied directly from the Eye of Terror itself, linking the Emperor of Brass to far more dangerous threats.
At the end of the conflict, the once-rich worlds of the Gelmiro Cluster had been reduced to smoking remnants of ruin and shame. Many planetary populations had become nothing more than scav-mutants, doomed to wander across the devastated wastes, surviving off the rotting remains of their once-great civilizations. The Imperial agencies of the Calixis Sector avoid the haunted worlds of the Cluster, now classified as war worlds, to this day.