My Sims of the Eastern Jin Dynasty

Horse hooves shattered the morning mist as dawn broke.

Xiao Heng pulled on the reins, and the twenty cavalrymen immediately lined up. The sound of hooves stopped abruptly, leaving only the rustling of the wind through the reeds.

Not far ahead, a peculiar fortified village came into view.

Unlike the refugee fortresses in Huaibei that barely protect themselves with rammed earth walls, this fortress is nestled at the confluence of three rivers, surrounded by water on three sides, with only a narrow dirt road about ten feet wide on the northwest side connecting it to the shore, resembling an isolated island in the water.

Shallow trenches were dug on both sides of the dirt road, and the trenches were connected to the river, with water flowing gently. This served both to block the enemy and to irrigate the fields.

The fortified village was surrounded by a three-tiered wooden fence, each as thick as a bowl. The base of the fence was buried deep underwater, and the tops were sharpened and wrapped with thorny vines, making it an impenetrable defense.

Even more conspicuous were the three watchtowers standing at the four corners of the fence, each about five zhang high. The towers were built of solid wood, and each level had observation holes and arrow holes. The sentries at the top of the towers held longbows, their eyes already locked on this cavalry team of unknown origin.

What's even more amazing is the scenery around the fortified village.

The Huaibei region is mostly barren fields and ruins, but here it is quite the opposite. The fields outside the fence have been cultivated in an extremely orderly manner, with crisscrossing ridges and several narrow irrigation canals that bring river water into the fields at just the right amount.

Seven or eight farmers were already working in the fields with their tools when they saw the cavalry and looked up at them.

Such an ingenious layout could not have been achieved by ordinary refugee fortresses; it must have been overseen by a skilled person proficient in defensive fortifications or concealed elite troops.

Xiao Heng remained silent, his gaze sweeping across the entire fortified village, his eyes filled with scrutiny and amazement.

He knew he had come to the right place. Based on this planning approach, it was far superior to the camp set up by Han Yong and his men, and even inferior to Deng Jing's.

Having spent many days in the Huai and Si regions and become accustomed to hastily constructed and easily destroyed fortified villages, this design, which takes into account defense, irrigation, and people's livelihood, is truly rare.

Especially the moats connected to the river and the well-organized irrigation canals, which could not have been built by brute force, must have been the work of someone knowledgeable in hydrology and skilled in calculation.

At this moment, the sentry on the watchtower had already sounded the alarm. A crisp clapper sound pierced the morning sky, and more than ten strong young men carrying spears immediately poured out from behind the gate of the fortress. They formed a neat defensive line and guarded the entrance to the dirt road. The leader was dressed in a short brown robe with a leather belt around his waist. He held an iron blade in his hand, which looked like a butcher's knife. He looked at Xiao Heng warily.

"Who are you?"

The man had a loud voice, and although he was unarmored, he stood upright like a pine tree, unlike ordinary refugees.

Xiao Heng raised his hand to signal his guards to relax. He dismounted and walked slowly forward, his voice steady and powerful:

"I am Xiao Heng, the Prefect of Donghai. I have temporarily stationed my troops at Huaipu. I have come here today not to provoke trouble, but only to see the person in charge of the fortress."

The man in the short brown robe looked somewhat surprised, clearly having heard of his name. He turned and gave a few instructions to the man behind him, who immediately turned and ran back to the fortified village. Then, he turned to the side and raised his hand, saying, "Lord Xiao, please wait a moment. My master is inspecting the water conservancy project. Please allow me to inform him."

Xiao Heng nodded, taking the opportunity to look around again.

He noticed that the irrigation ditches along the fields were not dug randomly; their slopes were extremely gentle and the water flow was uniform, clearly calculated to ensure that every field could be irrigated without the water flowing too fast and washing away the ridges. The water flow at the base of the fence appeared calm, but it actually contained hidden whirlpools, suggesting that the river channel had been deliberately modified. If enemy troops were to attempt a wading attack, they would certainly be hindered by the water flow.

These details further confirm that there must be a genius in the dock who is proficient in water conservancy and mathematics.

About the time it takes for an incense stick to burn, the person who had just delivered the message returned quickly and whispered a few words to the man in the short brown robe.

The man's expression turned serious, and he said to Xiao Heng:

"Lord Xiao, my master invites you to the dock."

After saying that, he waved to signal the young men guarding the road to make way, but he still maintained a guarded posture.

Xiao Heng stepped onto the dirt road. The soil under his feet was firm and had obviously been compacted, so it was not easy to collapse even on rainy, muddy days.

As he approached the gate, he looked up at the watchtower and saw that although the sentries were still keeping a close watch on them, they had put away their bows and arrows. He secretly praised the well-managed and disciplined state of the fortress.

Passing through two layers of gates, the scene inside the fortified village becomes more orderly. Rows of elm trees are planted on both sides of the road, and drainage ditches are dug under the trees to divert rainwater into the river. Although the houses on both sides are made of adobe and are not luxurious, they are sturdy and clean. Neatly stacked firewood is placed in front of each house. In the center of the fortified village is a square pool with clear water that is connected to the outer river. Several waterwheels are set up by the pool and are slowly turning, diverting water into the village's irrigation network.

Not far away, by a pool of water, a man in a blue robe was squatting on the ground, holding a wooden ruler in his hand, bending over to measure something.

He was about twenty years old, dressed in a blue cloth robe with the cuffs rolled up, revealing mud spots on his forearms. His hair was tied up with a wooden hairpin, and he had a handsome face with a focused expression. He was completely unaware that someone had arrived.

Beside him lay a roll of linen, covered with densely drawn lines in charcoal, resembling a river map, and marked with many strange symbols—the very same graphics Xiao Heng had seen in the exploration of the picture.

The man in the short brown robe coughed lightly and said in a low voice, "Sir, Lord Xiao has arrived."

The man in the blue robe suddenly looked up, his focus still lingering. Only after seeing Xiao Heng's attire did he slowly stand up, brush the dirt off his clothes, and bow in greeting.

"My name is Zu Chang, and I am the head of this village. I was unaware of Lord Xiao's esteemed presence and have failed to greet you properly."

"Zu Chang?"

Xiao Heng returned the greeting with a cupped hand, his gaze falling on the rolled-up linen picture.

"Mr. Zu, there's no need for such formalities. I was just passing through this place when I saw that this village was exquisitely laid out and the fields were neatly arranged, quite unlike any other place. I was filled with admiration for it, so I came to pay my respects."

Zu Chang followed his gaze to the hemp cloth, a hint of composure flashing in his eyes. He reached out and rolled up the cloth, saying, "In chaotic times, if you want to protect yourself, you can only rely on some rudimentary skills to renovate the fortified villages and cultivate the land, so that your clansmen and refugees can have a place to settle down. It's nothing special."

These words were spoken with great humility, but the tone revealed a high degree of confidence in one's own skills.

Xiao Heng didn't put on any official airs. Pointing to the symbols on the scroll, he casually asked a question.

"These symbols seem to be used to measure the depth of rivers and the slope of fields? Mr. Zu must have been quite knowledgeable in mathematics and water conservancy."

Zu Chang was visibly surprised, clearly not expecting Xiao Heng to be able to understand these symbols. These were calculation markings he had created himself based on the "Nine Chapters on the Mathematical Art" and the characteristics of the Huai River's hydrology; ordinary people would never know them.

He looked at Xiao Heng and then examined him carefully, his tone showing more approval, but still carrying a hint of arrogance.

"Lord Xiao has a good eye. That's right. The Huai and Si Rivers are covered with a dense network of waterways. If we can't accurately measure the hydrology and topography, the defense of the fortified villages will be as flimsy as paper, and the fields will be impossible to irrigate."

Xiao Heng only understood what these symbols were for after using a normal simulation. He didn't rush to win them over, but just stood there and observed them carefully.

Soon, he saw a mark on the map indicating a fork in the river channel, and then discovered three circles of different sizes, with faint counting rod symbols still marked next to them. It must be that they were calculating the diversion ratio at different water levels. Xiao Heng remained calm and quickly used the simulation again. After a few breaths, he took a closer look at the symbols and understood.

"Sir, are you calculating the separation of water storage in the pond and irrigation canals?"

Zu Chang was even more astonished this time, and he nodded.

"Indeed, with the recent increase in rainfall, there is a risk that the ponds will overflow and flood the surrounding houses. We need to calculate a precise diversion ratio to both conserve irrigation water and prevent flooding, but..."

He frowned slightly, his tone tinged with helplessness.

"This method requires counting rods to deduce step by step, which is time-consuming and laborious. Moreover, the error becomes quite large when we reach the third fork. We are worried about how to calibrate it."

Upon hearing this, Xiao Heng's heart stirred; the opportunity that had appeared in the simulator had arrived.

He squatted down, picked up a twig, drew a right triangle on the mud, and then drew two similar small triangles next to it. He looked up at Zu Chang.

"Do you know that for triangles of the same shape, the corresponding sides are all proportionally identical?"

Zu Chang was taken aback. He bent down to examine the pattern on the mud more closely, his brows furrowing even more. He then looked up at Xiao Heng.

I repeatedly recalled that in the Nine Chapters on the Mathematical Art, the proportions of the right triangle are 3, 4, and 5, but it never mentioned that the proportions of the corresponding sides are all the same.

Xiao Heng smiled, not giving him a chance, and pointed to the three sides of the triangle with a twig.

"This is the large triangle, and these two are the small triangles. The three are the same shape, only different in size. They can be used to measure the slope of a river and the depth of a pool. There is no need to repeatedly use counting rods to deduce the results. Just measure the length of one side, and you can calculate the rest of the sides."

After speaking, Xiao Heng could tell from Zu Chang's expression that he had taken it to heart. Without giving him time to think, he wrote a simple formula on the ground, which was the proportional formula for similar triangles in modern mathematics, and then pointed to Zu Chang's burlap diagram.

"For example, if you want to calculate the proportion of flow at the three bifurcations of the river, you don't need to calculate and accumulate the results one by one. You can first measure the width and depth of the main channel, then measure the width of each bifurcation channel, calculate the depth using similar proportions, and then calculate the flow rate. This method is three times faster than the calculation method, and the error can be reduced to within millimeters."

Zu Chang's breathing gradually became rapid. He stared intently at the triangle and equation on the muddy ground, his fingers tracing patterns on the diagram as he muttered to himself.

"If that's the case... then wouldn't the water volume of the pool also be simplified using this method? We wouldn't need to measure it in sections; we could simply measure the circumference of the pool's opening and its depth to calculate the total?"

"Exactly."

Xiao Heng couldn't help but admire him, and then nodded and added.

"A pool of water is roughly cylindrical, and the volume of water it holds is equal to the area of ​​its base multiplied by its height. If the area of ​​the base is difficult to calculate, first calculate the diameter from the perimeter, then calculate the radius, multiply the radius by the radius, and then multiply by the circumference of the diameter to get the area of ​​the base. This method is more time-saving and accurate than calculating it in sections."

"Wednesday Path One?"

Zu Chang suddenly looked up, a glint of light flashing in his eyes.

"Sir, are you saying that the circumference of a circle is three times its diameter? But the *Zhoubi Suanjing* says that a circle's diameter is one circumference, yet no one connects this to volume measurement!"

He no longer cared about hospitality, turned around and rushed to the hemp map, picked up the wooden ruler and counting rods, and started calculating quickly while comparing the map on the ground. He even asked someone to bring a large pile of books. Xiao Heng also saw real ancient books, a dozen or so of them about mathematics.

Xiao Heng stood quietly to the side, watching him sometimes frown in thought, sometimes suddenly realize something, and sometimes excitedly search through the book full of annotations, his smile gradually deepening.

Half an hour later, Zu Chang suddenly stood up, his counting rods falling to the ground with a clatter, his face full of disbelief.

He walked quickly to the edge of the pool, measured the circumference of the pool with a wooden ruler, measured the depth of the pool, and then used the method taught by Xiao Heng to calculate the water storage capacity. The result was almost identical to his calculations in sections, but the time taken was less than a third of the previous calculations!

"A divine skill! This is truly a divine skill!"

Zu Chang's voice trembled with excitement as he bowed deeply to Xiao Heng.

"Sir, your talent far surpasses what I, Chang, have ever seen! I, Chang, was so arrogant before that I was unaware that such exquisite mathematics existed in the world!"

Xiao Heng quickly helped him up, his tone sincere.

"Mr. Zu, there's no need for that. This is the wisdom of our predecessors, and I am merely picking up scraps of their wisdom. You, sir, are truly a practical talent for governing the world by applying mathematics to the defense of fortified villages and the irrigation of people's livelihoods."

"..."

Two days passed in the blink of an eye.

Zu Chang's enthusiasm for these novel mathematical methods grew stronger, and he often discussed them with Xiao Heng until late at night.

Not only can they apply what they've learned to other situations, but they also have strong hands-on skills.

During this time, Xiao Heng also subtly mentioned that the people of Huaipu were displaced and that the Qin army was threatening them with a water attack. He implied that if Zu Chang had helped, Huaipu could become a safe haven in the chaotic world.

But every time this matter comes up, Zu Chang will change the subject or lower his head to do calculations, his expression full of hesitation.

On the morning of the third day, Xiao Heng packed his bags and prepared to leave.

These past two days, he's practically been pulling out Arabic numerals, but this guy is completely unresponsive. With his math knowledge almost completely forgotten, if he doesn't leave soon, there'll be no one left to teach him. Several times when he's been asked, he's only been able to give vague answers. But Xiao Heng knows that he can't really hide anything from someone with such talent.

The guards were already waiting at the gate of the fortress with their horses.

Xiao Heng lingered, wanting to see if there was still a chance.

Half an hour passed, but Zu Chang did not show up. He only sent someone to deliver a map of the Huai and Si rivers.

He mounted his horse, said no more, waved his hand, and twenty cavalrymen followed closely behind, slowly departing along the narrow dirt road.

Zu Chang stood by the pool, watching their figures disappear into the reeds, and looked down at the triangular shape on the muddy ground.

Xiao Heng's methods of mathematics were like a new window, allowing him to see the infinite possibilities of skills. However, he also knew that in chaotic times, perseverance was more difficult and more important than venturing out.

After traveling several miles, the captain of the personal guard couldn't help but ask.

"My lord, are we just going to let Mr. Zu stay like this? If we can make use of his talent, the defense of Huaipu will surely be greatly enhanced."

Xiao Heng reined in his horse and looked back towards Chenliuwu. The fog had shrouded it, leaving only the faint outline of the watchtower. He raised his hand and waved the map in his hand, a look of certainty flashing in his eyes.

"No need to rush. Although he didn't come with us, he gave us the most precious thing. Besides, I know he will come sooner or later."

Zu Chang's passion for mathematics and his concern for the common people were things that Xiao Heng valued. As long as he could make Huaibei a place where he could truly settle down, he believed that this genius would eventually leave that fortified village on his own initiative.