In this realistic war game, only I understand the course of the battle.

In the spring of the fourth year of the Yongle reign, Shen Du stood on a desolate open space south of Beiping City, with an endless expanse of yellow earth in front of him.

This will be the southern city wall of the new capital. According to Zhu Di's decree, the new capital would be larger than the Yuan capital—the palace city in the center, surrounded by the imperial city, with a square inner city and an outer city providing protection. The city walls were not made of rammed earth, but of large blue bricks fired in Linqing, Shandong, each weighing forty-eight jin (approximately 23 catties), grouted with lime and glutinous rice paste. The gate's heavy gates were forged from refined iron by the Nanjing Arsenal, with water-filled holes above the gate openings so that water could be poured down from the gate towers to extinguish fires set by the enemy. Each city gate would also have a barbican built outside, its walls lower than the main city wall, forming a semi-enclosed pit—once the enemy breached the barbican, the defenders could fire down from three sides from the main city wall, turning the barbican into a slaughterhouse.

"Lord Li, the foundation for the south city wall has been dug, but the soil underneath is looser than expected during the survey." A sweating official from the Ministry of Works jogged over, holding a soil sample just retrieved from the foundation pit. Shen Du took the sample, squatted down, and crushed it with his fingers; the proportion of sand was indeed too high. He tasted the sample—it was salty. The groundwater level was higher than during the survey, and the salinity was seeping upwards; if the foundation wasn't treated, it would subside in a few years.

"Dig three feet deeper, down to the hard soil layer." Shen Du stood up, threw the soil sample on the ground, and patted the soil off his hands. "Lay three layers of gravel at the bottom of the pit and tamp them down. Then lay a layer of lime mixed with clay on top of the gravel, tamp it down, and then build the brick foundation. Add two more drainage ditches to this section of the city wall than the others, to divert the seeping alkaline water into the moat. The moat in the south of the city should be dug deeper than that in the north, directly to the waterproof layer." The official in charge of the Ministry of Works took notes on bamboo slips and nodded repeatedly.

Old Zhao squatted on a nearby pile of lime, a pipe dangling from his mouth, the smoke flickering in the spring sunshine. His trousers were rolled up above his knees, revealing two scarred calves, his bare feet sinking into the lime, his toes filled with white ash. He was no longer the leader of the obstacle-breaking team; he was now the foreman of all the craftsmen at the Xindu construction site—responsible for over three thousand craftsmen and laborers. From quarrying and brick-making to timber processing, every step required his signature for approval.

"Master Li—Lord Li," Zhao Laoliu pulled his pipe from his mouth and pointed with the pipe to a section of the city wall being built not far away. "Look at that wall. The bricklayers are from Shandong, and their skills are fine, but the ratio of glutinous rice water mixed in the lime mortar is wrong. It's too thin, and it won't be strong enough after it dries. One hammer blow and the bricks will pry out of the seams. I told them that the glutinous rice water needs to be boiled for two hours before mixing with the lime, but they thought it was a waste of firewood and were just trying to fool me." Shen Du followed him over to inspect it and immediately ordered that section of the wall to be demolished and rebuilt.

When Su Wanqing returned from the military farms north of the city, it was almost dark. She was wearing a faded blue cloth shirt with the sleeves rolled up to her elbows, carrying a roll of blueprints in her hand, her face flushed from the spring breeze. Behind her were several clerks sent by the Ministry of Revenue, each carrying a stack of account books—she was responsible for the accounting of all the grain and fodder allocations, artisan salaries, and material purchases in the new capital.

"The farmland outside the North City can yield two harvests this year. The winter wheat sown last autumn has already started to fill out, and the first crop can be harvested in May. All of this grain will be transported to the Xindu granary, enough to feed 100,000 craftsmen for half a year." She spread the blueprints in front of Shen Du, her fingertips tracing the route of an irrigation canal. "But there's a problem—the irrigation canal draws water from the Western Hills to the South City, passing through a section of gravelly land where seepage is too severe. We need to replace it with underground ceramic pipes. Ceramic pipes are more expensive to build than open canals, but in the long run, they will save water and labor." Shen Du looked at the blueprints and remained silent for a while. Then, he suddenly asked an unrelated question: "Does your father know what you're doing in the Northern Frontier?" Su Wanqing looked up at him, then continued looking down at the map, her voice soft and even: "Yes, he knows. He's the Provincial Governor in Shanxi, and I'm in Beiping doing my agricultural and water conservancy projects. He wrote to me saying that daughters are more useful than sons." After saying that, she opened the account book and wrote a few more lines, "I've calculated the cost of the pottery pipes. The extra money spent can be recouped within three years from the savings in water fees and repair costs. If you think it's acceptable, I'll have the Ministry of Revenue place an order tomorrow."

By the summer solstice of the fourth year of the Yongle reign, the city wall of Xindu had reached a height of two zhang (approximately 6.6 meters). The June sun beat down mercilessly on the construction site, making the blue bricks scorching hot. The laborers, shirtless, carried bricks, their backs peeling layer after layer from the sun, sweat dripping down their backs and leaving dark watermarks on the bricks, which dried quickly. Shen Du walked dozens of times a day on the construction site, his old injury on his left leg throbbing slightly in the heat. The ointment the army doctor applied to him was soaked through with sweat time and time again, but he never left early. Zhao Laoliu had several rows of sunshades erected on the construction site, under which were large vats of mung bean soup. The mung beans were specially approved by Su Wanqing from the Ministry of Revenue's granary, and dozens of pots were boiled every day, so anyone who was thirsty could scoop some out to drink. She also invited several old doctors from Shandong to perform scraping and bloodletting treatments on the craftsmen suffering from heatstroke.

That noon, Shen Du was squatting on the city wall discussing the angle of the crenellations with Zhao Laoliu when a messenger rode up from the north. Before the horse had even come to a complete stop, the messenger tumbled off. "Lord Li—His Majesty has arrived! The imperial carriage has reached the north gate!"

Zhu Di arrived incognito. Without entourage or an imperial carriage, he was accompanied only by a dozen personal guards and two Hanlin scholars. He rode north from Nanjing for nearly a month. Standing outside the north gate of the new capital, he looked up at the city wall under construction—the blue brick walls gleamed a calm gray-blue in the afternoon sun, the moat had been dug to the intended depth, and clear groundwater gurgled from the drainage outlets of several underground ditches. He walked a long way along the base of the wall, touching the mortar between the bricks, squatting down to examine the structure of the drainage ditches, and even climbing the scaffolding to inspect a section of the barbican under construction.

"You stood outside Jin Chuan Gate in Nanjing for a long time," Zhu Di said suddenly, standing directly atop the barbican. "You entered through Jin Chuan Gate, passed through that heavy gate, and then arrived at Fengtian Hall. Did you see the structure of that heavy gate?"

Shen Du stood half a step behind Zhu Di: "Yes, Your Majesty. When I was in Nanjing, I carefully examined the thousand-pound gate of Jin Chuan Gate. The gate is made of a single piece of cast iron, weighing over ten thousand pounds, and is raised and lowered using a winch and iron chain. The structure itself is not the problem—the problem lies in the triggering mechanism. The thousand-pound gate of Jin Chuan Gate requires the guards on three city towers to turn the winch simultaneously to lower it, and it takes at least several dozen breaths from the order to lower the gate to the ground. When Li Jinglong surrendered the city, he did not give the guards any time to lower the gate, rendering it useless. I have improved the design of the thousand-pound gate in Xindu—I have embedded a separate hidden compartment mechanism in the inner wall of the gate opening. As long as one person pulls the iron pin, the thousand-pound gate will fall directly from above, without the need for multiple people to cooperate. There is also an independent winch set up on the city wall, and the two systems do not interfere with each other."

Zhu Di turned to look at Shen Du, a hint of scrutiny in his eyes. "You've turned the lesson of Nanjing's fall into the defense of the new capital," Shen Du said, bowing slightly without adding anything further.

In the autumn of the sixth year of the Yongle reign, the city walls of the new capital were fully completed. All eighteen city gates, fifty-four barbicans, and twelve thousand crenellations were finished. The palace walls of the Forbidden City were erected, and the foundations of the three main halls were being paved with the final layer of gold bricks. The moat, after being filled with fresh water, became a natural waterway, allowing southern grain transport ships to sail directly through the water gates at the foot of the imperial city. The project lasted several years, employing hundreds of thousands of craftsmen and laborers, and utilizing hundreds of millions of bricks, millions of cubic meters of stone, and hundreds of thousands of timbers, all sourced from over one hundred prefectures and counties across the country. Throughout the entire project, no large-scale casualties occurred—a point of great pride for everyone involved in its construction.

That year, Su Wanqing was officially transferred to the Ministry of Revenue, serving as the Chief Clerk of the Beizhili Military Farm and Water Conservancy Bureau. As the daughter of a former official of the Jianwen Emperor, she was not expected to be given a prominent position by the new dynasty, but after reviewing her plan for the northern frontier's military farms and water conservancy, Zhu Di remarked, "Talent transcends birth," and approved her appointment. Her first act upon taking office was to expand the military farms around the new capital from military households to civilian households, allowing displaced people to settle and cultivate the land around the capital, with the government providing seeds, farming tools, and a three-year tax exemption.

That year, Zhao Laoliu was promoted to Assistant Director of the Construction Department of the Ministry of Works—a sixth-rank official. He had never worn an official robe in his life, and on the day he received it, he wore it inside out, the rank badge facing backwards, which Shen Du laughed at for a long time. Standing atop the highest city tower in the new capital, pipe in mouth, he looked down at the new city that had sprung from the wasteland and remained silent for a long time. Then he tapped his pipe and said, "This life has been worthwhile."

In the first month of the seventh year of the Yongle reign (1402), Zhu Di officially issued an edict to move the capital, renaming Beiping as Beijing and Dadu as Shuntian Prefecture, with Beijing as the capital and Nanjing as the secondary capital. The edict was promulgated throughout the empire, and all civil and military officials, as well as the Six Ministries and Nine Ministers, moved to the new capital, Beijing. The grand ceremony for the relocation of the capital was held in the newly completed Fengtian Hall. Zhu Di sat on the throne, wearing a ceremonial robe with twelve imperial symbols, with the entire court of civil and military officials before him and a gilded screen carved with nine dragons soaring through clouds behind him.

Shen Du stood at the front of the military ranks, wearing a crimson robe befitting a fourth-rank official, embroidered with a cloud-and-leopard emblem. At the very front of the ranks stood Zhu Neng—now the Duke of Cheng, a hereditary title, who carried a sword into the palace. Zhu Neng's old wound on his right arm still ached on cloudy days, but his back was ramrod straight, and the old scar on his brow from the Jiahe River was faintly visible in the candlelight. Beside him was Chen Mao, the Marquis of Ningyang; and next to him was Huo Zhen, the commander of the Doyan Three Guards. These men had all followed Shen Du in countless charges, maneuvers, and desperate battles. Zhu Neng, who had patted Shen Du on the shoulder in Dezhou and said, "You're lucky, kid," now often said after military councils, "Old Li, you've drawn a new map again." Shen Du remained largely silent, simply standing ramrod straight beside his old comrades.

After the grand ceremony, Zhu Di kept Shen Du behind. Not in the main hall, but in a side hall of the Wuying Hall. Zhu Di removed his imperial robes and changed into a plain blue cloth robe. He sat behind a desk, on which lay a map larger than the previous map of the northern frontier defenses—this time a map of the entire country. From Liaodong to Annam, from the coast to the Western Regions, every frontier was marked on it densely.

"The defense system in the northern frontier is already in place. Beijing's city defenses are strong, and there is ample land for farming around it. The troops and grain reserves in Liaodong are also stable. But I am not only concerned about the northern frontier." Zhu Di's finger traced across the map from Liaodong southward, across the coastal areas infested by Japanese pirates, across the brewing rebellion in Annam, and across the various tribes in the Western Regions that had not yet submitted. "Every place on this map needs to be surveyed. We need people who understand both warfare and city construction to go and measure, to tell me how many soldiers, how much grain, and how many cities are needed there. My dear minister, would you be willing to travel to every corner of this map for me?" He withdrew his finger from the map and looked up at Shen Du.

Shen Du knelt on one knee, his clasped hands gesture as crisp and decisive as it had been on the training ground of the Broken City Camp years ago. "Your subject is willing to go."