They ran.

Little under one thousand pairs of ceramite boots thundered across the ground when the signal was at last given for them to advance, a bureaucrat in a distant command tent nudging the stylized 1 forward on a hololith table, orders transmitted through their helmet’s autosenses. As one, they blink clicked the notification away, and as one, they ran. This new breed moved in utter silence, giving no cheer or cry as they made for the battle that they had been made for.

Fresh fallen snow was already burying the bodies of the auxilia and Thunder Warriors who had made this breach possible, the superheated condensation from the destruction of the great gate cooling in the frigid air and falling back to earth, a violation of the natural order that stood as one of the lesser sins that man’s wars had done to the weather systems of their birthworld.  Wrecked vehicles and buildings were given only slightly more heed than the corpses that they trampled through, those onrushing boots soon enough coated in gore and debris. Soon enough the white-coated outskirts of Sanctii were replaced by paved and well-kept streets turned to ruin by a war that the average citizen of the city would never be given the dignity of understanding, and still they ran.

Through barricades and redoubts, abandoned or futilely held, they ran, brushing aside the fractured and panicking militias and regrouping defenders with a contemptuous ease. Relics of the Dark Age flashed their crimson beams of death, leaving only death in grim testament of what had come to Sanctii, while chainswords left their victims in far more grisly trophies. They were a people of contradictions, and this displeased Vairya. She absentmindedly thought of this as she wrenched her weapon free of the shattered sack of meat and bone that had once been a man, continuing onward without a word or concern for his carapace-clad comrades - the others would deal with them in turn. Now, the most important thing was to continue on, not waste her focus upon the fates of shopkeepers and housewives pressed into service. True, they bore mighty weapons and had felled many of those under her command - 82 according to her helmet - but that did not make them worthy of concern or recognition.

She continued to run as she thought over her own displeasure. It was a novel thing for one such as her. One of the first to pass through the perfected process that turned men into demigods, the Mistress of the First had practically grown up inside of the Emperor’s gene-labs, taught via hypnoindoctrination and obedient to the dictates of the Imperial Truth. Yet, as the motor of her chainsword finally quieted after she had released her finger from the trigger, she could not help herself. She despised this.

Not the weapon itself, no, it was a fine thing - a tool fit for its purpose, much as she was. But they were of different purposes, that was what was important. It was a weapon of her predecessors, a weapon that was built not to merely kill the enemy, but to be so brutally demoralizing in effect that all who saw one fall prey to its chain would quail in terror. A weapon to break ones enemy, to make rebellion and resistance as impossible to consider as healthy souls avoided the yawning void of oblivion. Is this what she was? Yet she was taught no jeers, no cries, no taunts, nothing like the warriors of the other First. She and her siblings killed in silence.

Perhaps they were flawed. A certain amount of cold logic supported that thought, even if a deeper part of her railed against the very notion. Was she, and the other firstborn scions of the gene-forge, missing some critical element of their design? Was she merely the last proof of concept before the true Astartes? Was this lacking essence going to condemn her to break apart in the crucible of the wars to come? All around those not quite good enough fell to pieces, the prototypes of the immortal judging a blow off by a centimeter, reacting a half second too slowly, and they died for it. She thought nothing of them, falling as they did in service of their duty. Would those who came after think the same?

A bevy of red-runes in her helmet display informed her she was nearing the factory complex, and she threw herself into cover as her attention turned to formulating a plan to breach the structure. She had lost nearly two-tenths of her total fighting force in between the initial bombardment and rushing through the blasted cityscape, having encountered negligible, threadbare resistance. Optimistic predictions from the Sigilites suggested a 50% casualty rate for the whole operation. Silently, Vairya blink clicked the report away.

In front of the scattered souls of the First Legion lay the beating heart of Sanctii’s industrial might, a sprawling manufactorum district nestled in the shadow of the city’s sprawling spire. Dimly, she remembered that in order to get here she and her Astartes had had to pass through one of the city’s primary hab blocks, but the battles there had never waged fierce enough for her full consciousness to have been activated, the wonder of the catalepsean node allowing her to sleep through the majority of the slaughter. It was here that they would face true resistance.

Volkite weapons spewed death at the power armored guardians ringing the building she had been tasked with claiming, the weight of fire increasing as all around her the surviving Astartes slammed themselves into cover, defaulting to suppression tactics while awaiting her orders. None of them had ever trained to do that, but each reflexively knew it was the appropriate response to the situation. They huddled tightly to their makeshift defenses as the foe returned fire, arcs of lightning and more esoteric projectiles flensing the very air as they traded shot for shot.

With only a moment’s hesitation, Vairya Kurus came to the decision that this was not the time for fine tactics or clever maneuver.  The broad street she and her Legion had holed themselves up in had once played host to far vaster hosts of workmen going to and from work and their homes, to say nothing of the gargantuan vehicles that shipped both raw and finished materiel. There was no protected avenue, and no capability for surprise. Perhaps if they had enough airlift they could’ve taken the roof, but she dismissed that thought out of hand. She had to work with the resources actually at hand.

Maps sprang to life in the vision of the assembled Marines, the Legion Mistress silently drawing her lines of advance as armor’s cogitator traced the movement of her pupils. A broad sweeping half-crescent, rushing forward into the grand factory hall that had, mere days ago, accommodated swarms of milling workers coming on and off shift. She had no doubt it would be well fortified by now, but it was the least bad option, presenting her with the greatest opportunity to make good her weight of numbers - assuming that the combination of speed and division of forces had given her the advantage in that regard, at least. If that was wrong, she would simply die faster. At least they would know quickly.

The Astartes continued pouring ruby-red fire into the manufactorum, none breaking cover as the plan was finalized. Fine lines delineating movements down to the squad level dominated their field of vision, orders and expectations absorbed before being acknowledged and hidden, the host silent and impassive behind their armor. Confirming, to herself if no one else, that this was the least bad plan she could devise with her current resources and information, Vairya blink clicked the rune to execute.

Some eight hundred bodies moved in response, either bolting out of cover in a sudden charge or moving themselves into a superior firing position. They were met by a fusillade in turn, the professional defenders of Sanctii better armed and better trained than the hapless militias who the Astartes had slaughtered in the hab blocks. In that exchange the last embers of the calamitous conflicts of the Dark Age flared once more into life, a war of man against machine with the deadliest arms crafted by either. Pure heat boiled men alive inside of their suits, while others simply died without a mark upon their armor as their nervous systems suffered fatal cascades. Millennia of research and enhancement in materials science and biomimicry safeguarded some from localized conduits of radiation as they moved in the moment between the trigger being pressed and the weapon responding, while pools of sludge and ash marked the passing of those who had been less lucky.

It ended with the cruelty and barbarism that only Old Night could bring. Crude motors roared to life as chains began to whirl upon their track, monomolecular edged teeth whirring into constant motion that was slowed only by the grinding of metal against metal when they began to bite into the power armor of Sanctii’s defenders. They had no such issue when they at last began to dig into flesh and bone. The bodies of men who had fought to preserve a beacon of peace and stability within the wastes were left where they had fallen in so many butchered pieces, and what remained of their murderers rushed forward.

They had arrived within the manufactorum complex itself, and now the true difficulties began.

A top-level subroutine of Deep Winter was in charge of the manufactorum network, and it dutifully sent a priority alert to its parent program as it began a threat analysis. Reviewing the combat data from the prior engagements, it immediately discarded any notion of its human auxiliary production capacity defending the installation, and instead began sitewide evacuation protocols. They had been unnecessary from the very start, but they served the important role of making the humans feel useful.

Right now the meat would just get in the way.

The Astartes breached the facility to a dulcet voice instructing them to make their way to the nearest exit point, soft-light holograms directing them to safety. Dimly, Kurus recognized that the arrows were pointing away from her and her legionnaires. A blick-click later and the gene-warriors fanned out into a vast loading hall in finely tuned rows, providing each other with overlapping fields of fire and minimizing blindspots.

It was a pointless exercise here, in this space where millions of workers had trudged in and out. The danger wasn’t going to be here. She knew this, but the very thought of laxity, of not treating every space as the pinnacle of danger, galled her on a level so fundamental it might as well have been etched onto her bones.

Deep within the bowels of  the massive factory complex, automated fabricators feverishly went to work. All safeguards had been disabled, all authorizations given, and there were no pesky foremen or overseers who thought themselves in charge of the glory of the machine to be shocked at what was being forged. In the darkest days of human history, in those times when stars were reduced to cinders and planets so much dust, when Mankind fought against its most deadly child, weapons were designed with the coldest of cruelty - to kill with the utmost efficiency, to eliminate any threat in accordance to the rigid laws of logic.

Squad after squad departed into the depths, and one by one vanished from the rune-map in the Legion Mistress’ auto-senses display. Reports were scattered and varied as she followed towards the facility’s central cogitation stack. Occasionally there was nothing at all, save for a spike of hard radiation on the auspex and a vox feed unceremoniously cutting out. What did come through was bad enough as it was - nanoswarms that swam through the air so thinly they passed in between the very sinews of flesh and bone before suddenly erupting as a solid spike in the bodies of her Astartes, neutron emitters operating at such an intensity that they reduced the frail flesh within the ceramite power armor to slurry while leaving the armor intact, and yet more esoteric weapons and traps of humanity’s scourge.

Her chainsword was magnetized back onto her back, the Legion Mistress realizing with a start that she didn’t even remember putting it away. It was a toy in these warrens of death, the vast halls reducing swiftly into cramped chambers and accessways, comfortable enough for the human components of Deep Winter’s industrial might to walk between their various duty stations, but hideously small for gene-augmented warriors in power armor. Movement out of the corner of her eye registered in a hypnoindoctrinated reflex before her conscious mind could process it, but that was no concern. Muscle inducers activated, accelerating the swing of her arm as she pulled the trigger on her volkite emitter, a beam of heat instantly melting the crystal-stack processor in a battle-automaton that had been approaching.

Fire and death surrounded her in a fraction of a second as the exchange played out around her command squad, serpentine mounds of metal covered in impossibly thin plates of armor with bizarrely slender weapons collapsing from the ceiling. Two of her own had fallen in the impossibly fast combat, their torsos simply nonexistent, as if they were nothing more than paper dolls with circles cut out of them by a particularly precise child.

An alarm went off in her helmet, noting that total casualties had passed fifty percent, before shutting off a moment later and then resuming again. Cross-referencing of the hive exterior map versus how far they had traveled so far indicated that they were entering the facility’s core, and a thought that had been nestled in her subconsciousness as she had half-slept while running through the wastes informed her that this was likely due to electromagnetic shrouding cutting her off from consistent contact with the bulk of her legion. She raised a fist, and her command squad at once came to a halt. A further hand motion saw an Astarte with a bulky backpack turn away from her and slump upon his knees, the Legion Mistress plugging her helmet into his vox-set. Overcharged, it should have enough power to punch through the interference, even if only once.

“Silence all vox. Initiate aetheric warfare protocols. The Raptor strikes.”

Her voice rasped when she began to speak, the flesh unused to such demands, but hardened at her final words. Brief vox squeals of affirmation followed in response, before they went dead as well, and the man knelt in front of her took off his backpack. It was already beginning to smoke from the demands it was placed under.

Another flurry of hand signs saw them move onward once more.

Death, and the signs of death, stalked their steps. Astartes had fallen in every way imaginable to a mind that thought nothing of morality or pride, the bodies of some forced to submit to novel biophages while others simply ended, phasing into walls and ceilings, a rare few marked by nothing but a sharp spike of local ozone and a chainsword etched death tally. Hundreds died to monstrosities of the past age, dimly seen and dimly remembered. The manufactorum itself became their enemy as they advanced, gantryways swinging away to deliver hapless invaders to death in vast vats of molten metal, walls rearranging corridors into killzones.

Yet again and again the volkite beams shot out, curtains of death unmaking machinations ranging from finely tuned molecular kill drones to vast battle automata. The noose was tightening, and the factory could only make so much, so fast.

Vairya blinked in surprise when she at last stumbled into a wide chamber again, the woman scanning the monumental sphere she found herself in. Other Astartes filed in above and below, and from all sides, the cogitation center having been built for the comfort and awe of the humans who supposedly ran it. This concession to the meat in the machine proved the only advantage that the First needed, the wide and free sight lines affording them the clean shots needed to destroy the flights of buzzing drones that had been the final guardians of the Standard Templates.

One thousand Astartes had made the march to Sanctii. Fewer than eighty walked out of it.