Li Shimin stood near the steps of the Taiji Palace, turning the glass lens over in his palm. The tactical and industrial applications were obvious enough that he did not need to think about it.
"Approved."
Yan Lide froze.
What? That's it?
He had spent three entire days preparing for this audience. He had calculated budgets until his eyes hurt, rehearsed arguments about the importance of craftsmen until he could practically recite them in his sleep, and even prepared himself to argue with half the court if necessary. Now all those carefully prepared words sat uselessly in his throat.
Before he could process what had happened, Li Shimin was already pacing across the courtyard, discussing logistics as though he had been considering the idea for months.
"The Directorate for Imperial Manufactories is only going to become more important," the Emperor declared, gesturing with the lens. "Since that is the reality, establish the academy immediately."
He turned back toward the stunned architect.
"If the young apprentices are not yet ready to step into the foundries or shipyards, then let them spend their first few years learning mathematics. Once they understand the numbers, then they can touch the hammers and anvils."
He nodded to himself, apparently satisfied with this arrangement.
"As for teachers, the solution is simple. Take the old master craftsmen whose backs have begun complaining louder than court officials. Put them in classrooms instead of workshops. Let them pass on what they know before they start forgetting things and telling everyone the same stories about their youth for the hundredth time."
Yan Lide's magnificent speech instantly collapsed. What came out instead was an incoherent flood of praise.
"Your Majesty's foresight is truly... extraordinary. I... this minister is speechless. Such wisdom... the fortune of the empire..."
Li Shimin laughed and waved him off.
"Save it, Lide. I know I'm brilliant. There's no need to repeat it every five minutes."
Then his expression gradually became serious.
"When this wave of reform finally settles and I build the Lingyan Pavilion to honor those who laid the foundation of this empire, your name will not be forgotten."
Yan Lide's eyes widened.
Li Shimin continued.
"And once we pacify the western frontiers and reopen the Silk Road, I will erect a Stele of Tang Artificers before the Imperial Ancestral Temple."
The architect simply stared.
"It will bear the names of men like Zhang Wansui and yourself. You may not ride into battle or return with enemy heads hanging from your saddles, but make no mistake. Men like you are the foundation of this empire. Without craftsmen, we would all still be living in mud huts while arguing about philosophy."
Yan Lide had no memory of leaving the palace. He only remembered feeling strangely light. His feet barely seemed to touch the ground as he drifted through the imperial city, half convinced that a strong wind might carry him straight into the clouds.
In an age that revered scholars and often looked down upon manual labor, the Emperor had just promised to honor craftsmen before the Imperial Ancestral Temple. The idea felt almost absurd. It was like suggesting that merchants should be made ministers. Or that vegetables might actually be good for one's health.
From the palace steps, Li Shimin watched the usually solemn Minister of Works practically skip out of sight like a child who had just been promised unlimited sweets and a new pony.
The Emperor chuckled. It was deeply undignified. Under normal circumstances, such behavior might have earned a lecture on proper decorum. Today, however, he found it rather delightful. It was nice to see someone genuinely happy for a change. The court contained entirely too many men whose favorite pastime was plotting against one another.
Li Shimin had been thinking about this academy idea ever since that strange light screen started showing him glimpses of the future. At first, he thought it was some kind of divine intervention. Or maybe he'd eaten something bad. The palace cooks had been experimenting with new recipes lately, and you never really knew what you were getting.
But after a few weeks of consistent broadcasts, he'd noticed something interesting about those future people. They didn't worship poets who wrote sad verses about unrequited love. They didn't worship philosophers who spent all day thinking about whether trees made noise when they fell. No, they worshipped the people who actually built stuff. The engineers. The ones with sawdust in their hair and calluses on their hands.
Think about it. Those Dongfeng missiles that could apparently cross entire continents without getting lost. The machines that reached the heavens and didn't immediately fall back down. The space station floating up there like some kind of celestial Airbnb. None of that was built by scholars reciting poetry in beautiful calligraphy. It was built by people who knew how to make things that actually worked, people who got their hands dirty and didn't complain about it.
Even the recent broadcasts showed the same pattern. Better horseshoes that didn't fall off after two days. Improved crossbows that actually hit what they were aimed at. Every single advancement came from craftsmen tinkering in workshops, covered in sawdust and sweat, not from scholars debating in libraries while sipping tea and looking down on manual labor like it was beneath them.
Then there was gunpowder.
Okay, technically that was the Taoists' discovery. They'd been playing with fire and chemicals for centuries, after all. But honestly, the line between Taoist and alchemist was getting blurry fast. Li Shimin had read Li Jing's reports from the field, and the old general was not a man prone to exaggeration. According to him, the Taoists at Wulei Temple weren't acting like priests anymore.
They were acting like a bunch of guys who'd accidentally discovered chemistry and were having way too much fun with it. Like kids who'd found their dad's workshop and decided to see what happened when you mixed everything together.
They'd stopped chasing immortality. Turns out drinking mercury wasn't the path to eternal life, who knew? And started actually testing things like normal people. Adjusting mineral ratios. Recording results when they weren't busy dodging explosions. Refining their methods. They were keeping detailed notes, tracking what worked and what blew up in their faces with spectacular results. The whole scientific method thing, basically, centuries before anyone had a name for it.
Interestingly, the baseline literacy rate among the Taoist clergy was actually higher than the average worker in the Imperial Manufactories. Li Shimin suspected that their ability to read complex charts and maintain rigorous written records was the reason they had managed to standardize the gunpowder formula so quickly. That, and a healthy disregard for personal safety.
The Tang already had a system for registering craftsmen, dividing them into apprentices and master craftsmen with fancy titles and slightly better lunch privileges. But Li Shimin was starting to think that wasn't enough. It was like having a library but only allowing people to look at the covers of the books.
After their last meeting at Ganlu Pavilion, Du Ruhui had pulled him aside for a private conversation. The minister had been thinking about those future technologies as well, and he had a theory.
"If future generations can build weapons capable of destroying entire cities and machines that fly like birds," Du Ruhui had said, "then their craftsmen must possess knowledge far beyond our own. If the Great Tang wishes to approach even a fraction of that level, our craftsmen need a proper education. We cannot simply keep teaching them by trial and error."
Which meant mathematics.
A great deal of mathematics.
The subject that had probably been making students miserable ever since someone first realized that two stones plus two more stones somehow equaled four and decided this discovery needed to be taught to everyone else.
Geometry. Calculation. All the things that made ordinary people's eyes glaze over.
And yet, judging by the future, those same numbers seemed to be the difference between a civilization that built wonders and one that still lived in mud huts.
So when Yan Lide showed up asking about the academy, Li Shimin saw his chance. He laid out the vision right there in the courtyard. No need for fancy presentations or lengthy debates. No need for the usual bureaucratic back-and-forth that could drag on for months.
Now it was up to the craftsmen to prove they deserved those coveted spots in the Lingyan Pavilion and their names carved on that stele for all eternity. No pressure, right?
Li Shimin's contemplation of industrial reform was interrupted by the arrival of his most pragmatic minister.
Du Ruhui practically jogged up the palace steps, looking unusually pleased with himself.
"The signal towers are operational already?" Li Shimin raised an eyebrow. "Are you certain?"
During the wars that had founded the Tang dynasty, Li Shimin had personally directed massive armies using flags, smoke signals, and mounted couriers. He knew better than anyone how difficult communication could be on a battlefield.
Simple orders were easy enough. Complex ones were another matter entirely.
The foreigners shown by the Light Screen had solved the problem with their strange mechanical arms and tiny alphabet. Twenty-six letters, done. Easy. Chinese characters, on the other hand, numbered in the thousands. Each one a little work of art that took years to master.
At one point, during an especially tedious court session, Li Shimin had tried to devise a signaling code himself. He'd given himself a headache that lasted three days and finally given up, deciding that some problems were just too hard to solve. Some things existed to torment emperors, and this was apparently one of them.
"Your Majesty should come and see for yourself," Du Ruhui replied calmly.
The man's expression practically screamed, I've done something clever again.
Li Shimin's curiosity was immediately piqued. Ever since the appearance of the Light Screen, he had developed a bad habit of wanting to examine every new invention with his own eyes.
He summoned several Jinwu Guards and followed Du Ruhui out into the city.
Soon they arrived at an open square. A tall wooden tower dominated the skyline.
"We have built five of these within Chang'an," Du Ruhui explained, pointing south. "Each tower is one ward apart and positioned for clear sight of the next."
Li Shimin narrowed his eyes against the sunlight. Sure enough, he could make out the silhouettes of several other towers stretching all the way toward the Zhuque Gate.
"I invite Your Majesty to send a message."
"How?"
"Simply write whatever you wish," Du Ruhui said, and for once there was a hint of excitement in his voice. "A courier will take it to the tower at the Zhuque Gate. Then we wait."
The test sounded simple enough.
"Junxian. Bring me a brush and paper."
The supplies were quickly produced. Li Shimin waved everyone else away and stood beside a stone pillar, writing a short sentence in neat, practiced strokes. He rolled the paper up and handed it to Li Junxian.
"Take this to the tower at the Zhuque Gate," the Emperor ordered. "The moment you deliver it, turn around and ride back."
Li Junxian saluted. Then he mounted his horse and galloped down the avenue, scattering dust and forcing pedestrians to leap out of the way.
A servant hurried over with a chair. Li Shimin sat down and immediately began calculating.
Chang'an was roughly thirty li from north to south. The distance from here to the Zhuque Gate was around twenty-six li. A round trip would be over fifty.
Li Junxian rode one of the finest horses in the imperial stables, but even the best horse could not gallop through the crowded streets of Chang'an without trampling a few merchants. And trampling merchants tended to generate paperwork.
Realistically, the trip would take at least one and a half quarters of an hour.
Li Shimin tapped the armrest impatiently.
"Light a three-quarter incense stick."
It was the standard military method for tracking short intervals. You cut an incense stick to a specific length, set it on fire, and let it burn. Three-quarters of a standard stick matched Li Shimin's mental calculation for Li Junxian's round trip.
As the fragrant smoke curled into the sky, Li Shimin watched the distant towers with burning curiosity. Next to him, Du Ruhui stood with his hands tucked into his sleeves, looking confident.
Li Shimin didn't have to wait long.
When the incense was about halfway burned, he was still calculating whether Junxian would make good time or get stuck behind a slow-moving cart, the northern watchtower suddenly came to life.
Three large flags unfurled from the tower, catching the morning breeze. Red, white, and blue. Simple, high-contrast colors that would be easy to see from a distance even if your eyesight wasn't what it used to be. No fancy designs, no complicated patterns. Just bold colors that screamed "pay attention!"
The flags slashed through the air in a harsh, rhythmic sequence. Left, right, down, cross. The motion was entirely alien, yet clearly structured by a rigid internal logic. The moment the first tower finished its dance, the second tower further down the line repeated the exact same sequence. The message cascaded across the skyline, leaping from tower to tower.
Within seconds, the final tower looming directly over the Emperor's courtyard waved two red flags in succession. The sequence was over.
A young officer scrambled down the ladder faster than a cat running from water and ran over to the Emperor, his face flushed with excitement and exertion.
"Your Majesty," the young man said, breathless, bowing quickly before handing over a slip of paper. "The message has been received and decoded."
Li Shimin took the paper. He unfolded it.
The handwriting was rushed and slightly crooked, but the characters were undeniable: Empress Zhangsun is in good health.
It was the exact phrase he had sealed and given to his bodyguard.
He looked at the incense. It was barely past halfway. Li Junxian was probably just now turning his horse around at the gate, if he'd even made it there yet. The signal had traveled twenty-six li in practically no time at all. It was like magic, except it wasn't. It was human ingenuity.
"How did you do it?" Li Shimin asked, genuinely impressed. He'd been skeptical. Emperors had to be skeptical. It was in the job description. But this. This was something else entirely.
Du Ruhui smiled, the kind of smile a man gets when his plan works exactly as intended. "Minister Fang and I tried to copy those mechanical arms from the Light Screen. Spent three days on it. It was impossible. Too many characters, too many possibilities. We were trying to fit an ocean into a teacup."
"So what did you do instead?" Li Shimin leaned forward.
"We realized we didn't need to send characters at all," Du Ruhui explained, his voice gaining energy as he got into the explanation. "Just numbers. Simple, straightforward numbers that anyone can understand."
Li Shimin raised an eyebrow. "Numbers? How does that help with Chinese characters?"
"Each character can be found by three numbers," Du Ruhui said, warming to his subject. "Page number, column number, character position within that column. The towers just send numbers. Wave the flags in the right pattern, and you've got your message. The receiving end looks them up in a predetermined book. Simple, elegant, and impossible to intercept unless you know which book we're using."
Li Shimin tugged at his beard, thinking through the implications. "But if someone intercepts the signals. If enemy spies manage to memorize the flag patterns."
"They'd need to know which book you're using," Du Ruhui said, his smile widening. "And we can change it daily if we want. Use Sun Tzu's Art of War one day, the Book of Songs the next, a random poetry collection the day after that. The signals stay the same. Numbers are numbers. But the meaning changes completely. It's like having a different lock on your door every day. Even if someone steals the key, it won't work tomorrow."
Li Shimin processed the mechanical genius of the system, his mind running through his active military briefings. Suddenly, a specific geographical map flared in his memory. He slammed his hand down on the armrest of his chair, letting out a sharp bark of laughter.
"This changes everything for the naval fleet!"
Just yesterday, Li Shimin had been reviewing a frustrating report from the eastern coast. The Tang naval forces had been ordered to explore and pacify the large island of Liuqiu. However, the operation had turned into a nightmare. The indigenous tribes of the island were fiercely territorial, using the dense mountain jungles to launch devastating guerrilla ambushes.
Because the island was incredibly narrow from east to west but stretched massively from north to south, the local warriors simply vanished into the central mountains and slipped across the ridge lines to strike wherever the Tang forces were weakest. The imperial warships patrolling the coast could not communicate with each other fast enough to coordinate a trap. By the time a messenger boat rowed from one fleet to another, the ambushers were long gone.
But if those warships were equipped with tall masts and colored flags?
The admirals could talk to each other across miles of open ocean in a matter of seconds. They could track enemy movements from the coast, relay coordinates instantly, and trap the mountain fighters in an inescapable pincer movement. The island's geographical advantage would be entirely erased.
Li Shimin looked up at the towering wooden structure.
"With this technology in our hands," the Emperor declared, "the island of Liuqiu will be integrated into the Tang empire before the winter snows fall!"