"An artisans' academy?"
Li Shimin rolled the yangsui (a fire-starting lens that concentrates sunlight) between his fingers, giving it barely a moment's thought.
"Approved."
And just like that, all the words Yan Lide had carefully prepared were swallowed back into his stomach, rendered entirely unnecessary.
Li Shimin even took the initiative to help Yan Lide flesh out the idea:
"The Directorate of Works will only grow more important. Since that is so, an artisans' academy may as well be established."
"Even if they cannot yet enter the workshops, they can first study mathematics, then move on to the techniques of craftsmanship."
"Elder artisans may retire into posts as boshi (doctoral instructors) and assistant instructors."
In the blink of an eye, everything Yan Lide had been holding back turned into a stream of heartfelt praise for His Majesty.
Li Shimin merely smiled and shook his head.
"When these matters settle, if I commission the Lingyan Pavilion, I will certainly not forget you, my dear minister."
"And also…" Li Shimin hesitated briefly, then made up his mind. "Once the Western Regions are reopened, I intend to erect a Tang Artisans' Stele before the Imperial Ancestral Temple, to commemorate men such as Zhang Wansui and Yan Lide."
"You may lack dazzling military merit, but you are the foundation of a flourishing Tang."
Yan Lide had no idea how he walked out of the palace gates. His feet felt light the entire way, as though he were treading on clouds, as if a single gust of wind might lift him straight into the sky.
Li Shimin stood beneath the doors of Taiji Hall, watching Yan Lide hop and bounce his way out of the palace city in an utterly unseemly state.
In truth, ever since encountering the luminous screen, Li Shimin had noticed how highly later generations esteemed artisans.
Whether it was that so-called "Eastern Wind Express," or the machines that could ascend to the heavens, or even the "Heavenly Palace"—all were creations of craftsmanship.
And just looking at the previous content shown by the light screen: horseshoes, improvements to bows and crossbows—what were these if not inseparable from artisans?
And then there was that fearsome gunpowder… ah, no, that one was the Daoists' handiwork.
But in practice, there was little difference. Li Shimin had read Li Jing's memorials; the old general remarked that the Daoists of Wulei Monastery were beginning to look more and more like gunpowder craftsmen.
They no longer clutched at so-called thousand-year-old elixir formulas, but instead honestly experimented—adding and reducing minerals, igniting and testing, keeping records and summarizing results.
The Daoists' overall literacy was even higher than that of the Directorate of Works, which might well explain why their progress in gunpowder experimentation had been so rapid.
Although, at the founding of the dynasty, there had already been regulations registering artisans separately—dividing "workers" into apprentices and higher-ranking craftsmen—Li Shimin now felt this was still not enough.
When the private gathering at Ganlu Hall had ended last time, Du Ruhui had shared a conjecture with him in private: the creations of later generations were so astonishing that one could imagine just how high the learning of their artisans must have been.
Thus, if Tang wished to reach the technical heights of later ages, artisans would have to study "learning for practical application."
That was to say—mathematics.
Just as Yan Lide came to see him, Li Shimin conveniently laid out this vision in full.
What remained was to see whether Tang's artisans could one day earn the right to enter Lingyan Pavilion and have their names carved into the Imperial Ancestral Temple.
What Li Shimin had not expected, however, was that the first to bring him good news was Du Ruhui.
"The signal towers are already complete?"
Li Shimin could scarcely believe it.
During the pacification of the realm, flag signals had also been used, so Li Shimin knew well how complicated the coding of those three-armed semaphores from later ages was.
Moreover, foreign scripts consisted of rearranged symbols, while Chinese characters were each entirely distinct.
He had pondered it himself, but in the end the complexity had driven even him to give up.
"Your Majesty need only follow this minister and see for yourself," Du Ruhui said.
Li Shimin had always been indulgent toward novel contrivances. Following Du Ruhui's instructions, he set out with the Jinwu Guards and arrived behind the imperial city, where he saw a watchtower.
"At present, five watchtowers have been erected within Chang'an, each standing one ward apart," Du Ruhui explained.
Li Shimin looked north toward the Vermilion Bird Gate and indeed saw, faintly, identical watchtowers spaced at intervals.
"Please, Your Majesty, send a message," Du Ruhui bowed.
"How do I send it?" Li Shimin asked eagerly.
Du Ruhui had clearly prepared for this.
"Your Majesty need only write the words to be conveyed and have the Jinwu Guards deliver them to the messenger at the Vermilion Bird Gate watchtower."
"In no time at all, the messenger at this watchtower will report the transmitted message to Your Majesty."
The method was easy enough to grasp. Li Shimin glanced around.
"Junxian, fetch brush and paper."
Taking the writing implements, Li Shimin dismissed those around him, swiftly wrote a single sentence, rolled it up, and placed it into Li Junxian's hand.
"Deliver this to the messenger at the Vermilion Bird Gate watchtower, then return at once."
Li Junxian accepted the order, mounted his horse, clamped his legs to its belly, and galloped off.
A eunuch immediately brought over a chair. Li Shimin sat down and began calculating silently.
Chang'an stretched over thirty li from north to south; from the imperial city to the Vermilion Bird Gate was roughly twenty-six li. A round trip would be about fifty li.
Li Junxian was, of course, riding a fine horse, but within the city he could not gallop at full speed. Just reaching the gate would take about a quarter of an hour.
Tapping the table that had been brought over, Li Shimin ordered,
"Light three-quarter incense."
This was Li Shimin's most common method of timekeeping—incense of varying lengths, lit as needed.
Three quarters should be roughly the time for a round trip to relay the message.
As the upright incense burned slowly, Li Shimin brimmed with curiosity, while Du Ruhui remained calm and confident.
They did not wait long. When the incense had burned halfway down, Li Shimin saw movement at the watchtower to the north.
Three enormous flags appeared—perhaps for convenience, they were nothing more than simple red, white, and blue banners.
They seemed to be waved in a specific sequence, tower to tower. Soon, the watchtower by the imperial city waved the red command flag twice, and then a junior officer slid down from the tower by ladder.
The officer ran up to Li Shimin, his face flushed with excitement, clasped his hands in salute, and presented a slip of paper.
Li Shimin unfolded it. Written in crooked characters were the words: "Empress Zhangsun is in good health."
This was exactly what Li Shimin had written on the note Li Junxian had carried away. He turned to look at the incense stick—only half had burned.
That was to say, from the moment the Vermilion Bird Gate watchtower received the message, it had taken almost no time at all to transmit it back.
"How was this done?" Li Shimin was now truly intrigued.
Du Ruhui smiled and explained at length.
According to him, he and Fang Xuanling had initially tried the semaphore arms shown in the light screen, but quickly abandoned the idea—Chinese characters simply could not be encoded in the same way as foreign scripts.
But as the two of them brainstormed at the office, they soon realized a mistaken assumption.
Books were everywhere—how could they not serve as codebooks?
The signal towers needed only to transmit numbers. A single character could be broken down into two numbers: the page number and the position on the page.
Li Shimin tugged at his beard.
"But with so many books—"
He immediately realized his own foolishness. Each signal station only needed to transmit numbers—why would it need books at all?
And even if enemies tried to spy on it, countermeasures were simple. One could use Sunzi for the first half of the month, the Book of Songs for the second, or arrange several books in a fixed sequence and rotate them daily.
Running through Du Ruhui's method in his mind, Li Shimin suddenly recalled a memorial he had read a few days earlier and slapped his forehead.
"Would this not be of tremendous use to the naval forces?"
The fleet had already begun probing Yizhou and had met fierce resistance from the island's natives.
Though they had sea vessels, reports from the front indicated that the natives moved through forests as if on level ground, exploiting Yizhou's long north–south shape to dart east and west. Naval communications at sea were difficult; strikes often came too late.
"If this is so, then Yizhou can enter Tang this very year!"
The more Li Shimin thought about it, the more feasible it seemed. He could not help but laugh aloud.
"This year, Great Tang opens new territory once more!"