Wu Zheng introduced him to the dead on the fourth week.

  "This is Lao Meng," he said, gesturing at a skeleton propped against what had once been a siege engine.

  The skeleton wore corroded plate armour and held, in its bony grip, the handle of a weapon that had rusted into an abstract sculpture of its former self.

  "He was here when I arrived. Seventy-three years and he hasn't complained once. Best neighbour I've ever had."

  Chen Xi watched the old man with the detached attention he reserved for phenomena he did not yet understand.

  Wu Zheng spoke to the corpses the way other people spoke to cats: casually, affectionately, with no expectation of response and no embarrassment at the one-sided nature of the conversation.

  "Over there — the cluster by the collapsed wall — that's the card game. I call them that because of how they're sitting. See? Four skeletons, arranged in a circle, facing inward. I like to think they died mid-hand. The one on the left was winning."

  "How do you know?"

  "I don't. I decided. Seventy-three years is a long time. You fill it with what you can."

  Chen Xi filed this under "coping mechanisms, long-term isolation, creative."

  He also filed it under "Wu Zheng, core characterisation: a man who would rather invent companionship than admit to loneliness."

  They were looting.

  Chen Xi disliked the word, but Wu Zheng used it without shame, and the activity itself was straightforward: the dead cultivators of the Silted Bones carried equipment, and that equipment contained residual energy, and that energy could be harvested by a living cultivator willing to spend time extracting it.

  Wu Zheng had been doing this for decades. The returns had diminished as the most accessible corpses were depleted, but the deeper areas — the ones Wu Zheng had avoided because the residual energy levels were high enough to be dangerous — were now accessible.

  Chen Xi's vortex could process energy that would have overwhelmed a standard cultivator's intake.

  So they went deeper, and Chen Xi treated each corpse as a dataset.

  He measured the residual Qi signature of every body they examined. He noted the cultivation level at death (estimated by Wu Zheng, who could read the signs the way a geologist reads strata), the type and condition of equipment, the position on the battlefield, and any technique residues that clung to the bones like fingerprints.

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  By the end of the first week, he had catalogued 312 corpses and built a statistical model of the battle that had created the Silted Bones.

  "Two armies," he told Wu Zheng over a dinner of spirit moss and something Wu Zheng called "stone lizard," which tasted like chicken raised on a diet of disappointment.

  Wu Zheng was an astonishing cook, which was not a sentence Chen Xi had expected to think about a man who'd been living in a graveyard for seven decades.

  The moss, fried in rendered lizard fat with crushed spirit stone dust as seasoning, was genuinely good.

  "Two armies," he repeated. "One significantly more powerful than the other. The weaker army was defending a position — you can see it in the formation density, they're clustered around a central point.

  The stronger army attacked from three directions. Based on the decay rates of the technique residues, this happened between eight hundred and twelve hundred years ago."

  "That matches the histories," Wu Zheng said. "The War of Scattered Stars. The Azure Dust Sect and its allies fought the Crimson Lotus Sect and its allies here.

  The Silted Bones was the final battlefield."

  "The losing side — the defenders — used techniques that are more sophisticated. Higher-frequency energy signatures, more complex structural patterns. They lost not because their methods were worse, but because they were outnumbered."

  Wu Zheng chewed his lizard slowly. "That is... not the version taught in the Azure Dust Sect."

  "I imagine not. But the bones don't lie, and the energy signatures don't have opinions. The data says the defenders were more skilled and the attackers had more people. Numbers won."

  They ate in silence for a while.

  The bruised sky darkened toward night, which in the Silted Bones meant the faint glow of residual Qi became more visible, turning the landscape into something that resembled a field of dying stars.

  "There's something else," Chen Xi said.

  He had been saving this. Partly because the implications were significant and he wanted Wu Zheng alert and fed when he delivered them.

  Partly because he was still constructing the argument and wanted it airtight before he presented it, because presenting a hypothesis before it was ready was a habit he had beaten out of himself in the third year of his doctoral programme.

  "The defenders' technique residues. Some of them are annotated."

  "Annotated?"

  "Marked. With a notation system. I found it on thirteen corpses in the inner ring — the ones who were closest to whatever they were defending.

  Their equipment has symbols etched into it. Not language. Not characters. The symbols are mathematical."

  Wu Zheng set down his food.

  "They're doing calculus," Chen Xi said. "A simplified form, with symbols I don't recognise, but the structure is unmistakable.

  Derivatives, integrals, rate-of-change notation. Someone in this world — someone who fought in this battle, a thousand years ago — was doing real mathematics."

  "That's impossible. Mathematical notation of that kind doesn't exist—"

  "It did exist. It exists right there, etched into the armour of a dead woman in the third row. And it doesn't exist anymore.

  Which means it was destroyed. Erased. Someone, at some point in the last thousand years, eliminated mathematical knowledge from this world's cultivators."

  The silence that followed was different from the comfortable pauses in their conversation. This silence had weight.

  "Why?" Wu Zheng asked.

  "I don't know but I intend to find out. And in the meantime, I intend to translate those annotations.

  Because if those defenders were using calculus to design their techniques, then somewhere in this graveyard there is a technique manual written in a language I can actually read."