Chapter 272 — The Greatest Betrayal
Tony frowned slightly.
"What is the Horus Heresy?"
He looked directly at Gaius as he asked it, as though he expected the answer to be simple and immediate. But the question itself carried something heavier than curiosity. A heresy that had brought humanity into ignorance for ten thousand years was not the kind of thing that sounded possible at first hearing. It sounded exaggerated. Unreal. Almost impossible.
The workshop seemed to quiet even further around them.
Gaius did not answer right away.
He looked across the table for a moment, as if deciding how much needed to be said and in what order. Then he let out a slow breath.
"The Horus Heresy was the greatest civil war in Human history."
His voice was calm, but there was a weight to it now that had not been there when he had spoken of the Emperor or the Primarchs. The words settled over the table, heavy and exact.
He continued.
"It happened during the Great Crusade, when the Emperor was reunifying Humanity and building the Imperium."
He paused just long enough for that to land.
"At that time, the Primarchs commanded the Legions. The Imperium was expanding rapidly. Humanity stood on the verge of a golden age."
Halsey listened carefully, her expression focused and intent. The phrase golden age stood out to her immediately. In her experience, people used those words far too casually. But Gaius did not sound casual. He sounded like someone describing a civilization that had truly believed the future was within reach.
Then he continued.
"And then Horus betrayed the Emperor."
The room went silent.
Naruto frowned immediately, clearly trying to place the name in his head as something more than just a title. "Just one guy?" he asked, the disbelief in his voice obvious.
Gaius shook his head.
"Not one man."
"One Primarch."
He let the words settle before going on.
"He was the favored son, and the Warmaster of the Imperium. He is the second highest command next to the Emperor."
Tony's expression grew more serious at once. The title alone was enough to make the scale of it clearer. This was not just another commander turning traitor. This was one of the central figures of the entire civilization.
Gaius kept going.
"Half of the Imperium followed him. Half remained loyal. The result was a war that engulfed the galaxy."
No one spoke for several seconds.
Even Tony looked unsettled now, the weight of the scale finally breaking through his usual composure. A conflict involving half of an empire that ruled a million worlds was difficult to even imagine. It was not the kind of war humans were built to easily understand.
Halsey broke the silence first.
"How does something like that happen?" she asked, her eyes still fixed on Gaius. "You described the Primarchs as the Emperor's sons. The leaders of entire Legions. What could possibly make them betray everything they built?"
Gaius was silent for a moment.
Then he answered in a single word.
"Chaos."
The workshop grew quiet again.
Naruto frowned, looking from Gaius to Halsey and back again. "The same Chaos you talked about earlier?"
"Yes," Gaius said.
He gave a small nod.
"The Ruinous Powers targeted the Primarchs."
Tony blinked and raised a hand a little, as if needing to slow the conversation down before it spiraled too far ahead of him.
"Hold on," he said. "You mean those Warp gods managed to corrupt the Emperor's own sons?"
"Yes."
The answer came immediately.
Tony stared at him for a moment, clearly trying to fit that into what little he knew of the Warp and of Gaius's world. He had already seen enough to know those forces were dangerous. He had even seen a broadcast of Roboute Guilliman before, during the ceremony when Gaius had become a Praetor. That was all. Just a glimpse. But even in that brief glimpse, the presence had been unmistakable. Strength. Solemnity. Something immense. Something that felt bigger than the frame it occupied.
And yet even that had not prepared him for the idea that such beings could be corrupted.
"That's insane," Tony muttered. "The strongest people in your entire civilization. And they still fell?"
Gaius looked at him.
"Yes."
His expression remained calm, but not cold.
"But that is precisely why Chaos is so dangerous."
He folded his arms slightly as he continued.
"It does not require armies. It does not require fleets. It only requires weakness."
Halsey's eyes narrowed.
"A psychological attack," she said.
"In part," Gaius replied.
Then he named the things Chaos preyed on.
"Doubt. Pride. Ambition. Anger. Despair."
He looked across the table at all of them as he spoke.
"The Ruinous Powers exploit every flaw they can find. Even in Primarchs."
For a moment nobody said anything.
Mindy was the first to break the silence.
"So you're saying your greatest heroes became your greatest enemies?"
Gaius looked at her.
"Yes."
His answer came without hesitation.
"Some of the Emperor's finest sons became monsters."
That left another silence hanging in the room, heavier than the last.
Then Tony spoke again, his expression more serious now than it had been since the conversation began.
"What happened then?"
He had moved past casual curiosity. Now he was listening like someone trying to understand a disaster well enough that it could be recognized if it ever came close again. Gaius had already said there was always the possibility of a future mission involving his universe. If that happened, then this knowledge would matter.
Gaius remained still for a moment before answering.
"The Imperium burned."
The simple statement drew everyone's attention completely.
"The war spread across the galaxy," he said. "Brother fought brother. Legion fought Legion. Worlds were devastated. Entire fleets were annihilated."
His voice never rose. That made it worse somehow. There was no dramatic strain in it, no forced emphasis. Just the plain recitation of something that had truly happened.
"Trillions died."
Naruto's eyes widened slightly.
"Trillions?"
Gaius nodded once.
For a moment, nobody spoke.
Halsey's expression tightened.
Before the Covenant War, Humanity in her own universe had numbered only in the tens of billions. Even at its height, it had never come close to a trillion, nowhere near it.
The Imperium was different. She already knew it spanned more than a million worlds. A population measured in the trillions was not difficult to imagine.
Trillions of deaths, however, was another matter entirely.
The scale of the conflict required to produce losses like that was almost impossible to comprehend.
Mindy's mischievous attitude vanished.
The number was simply too large to picture. She tried anyway and immediately failed. Every disaster she could think of seemed insignificant compared to what Gaius had just described.
Tony remained quiet, his arms still folded.
Trillions of casualties were difficult to even comprehend.
"Likely far more."
Gaius went on before anyone could interrupt.
"The Horus Heresy was not a war fought over a single planet or a handful of systems. It engulfed much of Human civilization."
Halsey remained silent.
She had studied military history. She understood what civil wars could do to nations. Resources were destroyed. Infrastructure collapsed. Knowledge was lost. Recovery could take generations.
But the Imperium was not a single nation.
It spanned a million worlds.
Trying to imagine a civil war on that scale was difficult. The logistical damage alone would have been catastrophic. Entire fleets, industries, and planetary governments could have been wiped out.
Tony folded his arms.
"So how did it end?"
Gaius looked toward him.
"With the Siege of Terra."
Halsey immediately translated aloud, almost automatically.
"Earth."
Gaius gave a small nod.
Tony narrowed his eyes a little.
"And what about the other Primarchs?" he asked. "Not all of them were corrupted, right?"
For the first time in the conversation, Gaius paused.
"That is correct."
His tone became more measured now.
"Not all Primarchs fell. There were those who remained loyal to the Emperor."
Halsey's eyes sharpened slightly as she processed that.
"So the war wasn't simply traitors versus loyalists," she said. "It was divided even within each side."
Gaius nodded once.
"Yes."
He let the answer stand for a moment before adding,
"The Imperium was split in half… but even those halves were not unified."
Naruto frowned.
"That sounds like chaos even without Chaos."
Gaius did not deny it.
"It was."
Tony leaned forward slightly.
"So who stayed loyal?"
That was the question the others had been circling around without quite asking. If the Imperium had fractured that badly, then there had to be some forces that held together long enough to matter.
Gaius answered with the same quiet certainty.
"The Ultramarines remained one of the largest loyalist forces."
Halsey glanced toward him immediately.
"Your Legion."
"Yes."
"They were far from Terra when the betrayal began, but they regrouped and fought their way back across the galaxy."
He paused briefly, then added,
"The White Scars also remained loyal. They broke through the Warp storms and fought their way toward Terra at extreme cost."
Tony nodded a little, following carefully.
"And the others?"
Gaius's expression darkened slightly.
"The Imperial Fists made Terra itself their fortress."
He looked up slightly, as though seeing the events clearly in his mind.
"They would not abandon it under any circumstance."
Naruto blinked, trying to make sense of that image.
"So they basically turned Earth into a last stand?"
"Yes."
Gaius nodded once.
"That is accurate."
He fell silent for a moment, then continued.
"And then there was Sanguinius."
Tony heard the name and immediately looked up.
"Sanguinius?" he repeated.
His gaze shifted back to Gaius with renewed curiosity.
"A Primarch?"
The question hung in the air.
The workshop fell quiet.
Halsey watched Gaius closely.
Tony's attention remained fixed on him.
Even Mindy looked interested.
After a brief pause, Gaius looked at them all with the same steady seriousness he had carried throughout the discussion.
"Sanguinius is the Primarch of the Blood Angels."
Mindy blinked.
"The Primarch of the Blood Angels!"
Her reaction came quickly, still recalling their earlier discussion about the "armored vampires," as she had jokingly called them.
~~~
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