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

After the sandstorm at Jiahe subsided, the Yan army spent an entire day taking inventory on the south bank of the river. Captured muskets piled up like small mountains, and abandoned armor and weapons from the Southern army stretched from the riverbank all the way to the edge of the locust grove. Sheng Yong's central army banner, its flagpole severed by Zhu Neng, still stood atop the slope, half-flecked limply in the breeze. But the Yan army had no time to celebrate. Zhu Di's arrow wound reopened during the river crossing and charge. While the army doctor changed his bandages, he was studying a map; after the doctor left, he was still studying the map. News of the victory at Jiahe reached Beiping, and the civil and military officials left behind submitted memorials requesting the prince to return to rest and regroup. Zhu Di pressed all the memorials to the corner of his desk, writing only two words—"Go south."

He stood on a high slope on the south bank of the Jiahe River, facing the battlefield where fierce fighting had just taken place, and in the distance, the direction of the retreating Southern army. Sheng Yong had retreated to Dezhou, but he had lost over 100,000 men, and the city's food supplies wouldn't last long. Tie Xuan was still in Jinan, but the city walls hadn't been fully repaired from the Yan army's artillery fire and tunnels. Ping An's 200,000 troops had been divided and stationed in Cangzhou and Hejian after the Battle of Dongchang, diluting his strength. Wu Jie was in Zhengding; he was the last major general Jianwen could mobilize in Hebei.

"We cannot stop." Zhu Di said to the generals in the tent, his voice not loud, but every word carried an undeniable determination. "Sheng Yong has just been defeated, Tie Xuan has not yet been reinstated, and Ping An has divided his forces—the court's defenses in Hebei have already been breached by us. If we don't fight now, it will be too late for us to march south once Sheng Yong and Wu Jie join forces."

Zhang Yu died, and Tan Yuan died too. When Zhu Di went to war, two of his most familiar faces were missing from his command, but he showed no hesitation. He promoted Zhu Neng to the position of vanguard commander and added Chen Heng's son, Chen Mao, to the command ranks. Then he made a decision that no one expected—to have Shen Du attend the central army council.

When Shen Du entered the central command tent, he was still clutching a newly drawn topographical map of the Hutuo River ferry crossing. His armor was covered in mud, and his left leg was slightly lame. After entering the tent, he did not exchange pleasantries, but spread the map on the table and drew a line along the Hutuo River with his finger.

"Sheng Yong retreated to Dezhou, but he is not our next target." Shen Du's finger moved westward from Dezhou, stopping at the location of Zhending. "Zhending. Wu Jie has stationed 20,000 elite troops in Zhending, and a detachment of Ping An is also patrolling near Zhending. Zhending is the back door of Jinan—if we take Zhending, Jinan will be completely isolated. We can't use feints to attack Zhending like we did with Dezhou; Wu Jie won't fall for them. But Zhending has a weakness that neither Dezhou nor Jinan has—the Hutuo River flows around the city, and the terrain outside the city is higher than inside. If we build a dam upstream to store water, releasing the water will wash away the outer defenses and moats."

Zhu Di looked up at the young centurion. Shen Du had already mobilized scouts from the Doyan Three Guards, thoroughly surveying every canal and every abandoned riverbank near Zhengding. "Proceed as you suggested. The vanguard will still be led by Zhu Neng, and you will oversee the actual siege," Zhu Di said, tapping his finger on the location of Zhengding.

After two days of rest, the Yan army marched south, their advance aimed directly at Zhengding. Scouts who had set out ahead conducted a thorough search along both banks of the Hutuo River to ensure Wu Jie had not laid an ambush outside the city. Zhu Neng led the main force of 20,000 infantry and cavalry in close pursuit, with Shen Du's centurions and Huo Zhen's mounted archers leading the vanguard. Zhao Laoliu kept reciting the hydrology of the Hutuo River—he had worked on dikes with river engineers before mining coal in Datong and knew how to use water attacks. Shen Du had ordered him to lead men upstream to scout the location for a dam. When Zhao Laoliu returned, he spread out a rough sketch covered in muddy fingerprints beside his warhorse, his eyes gleaming: "There are three locations for the dam. Two have too loose soil, and one, on the foundation of an old dike, is best for water storage. Give me auxiliary troops and engineers, and it can be filled in two days."

Wu Jie stood atop the city wall of Zhen Ding, watching the approaching dust and smoke, his face calm and composed. He was a veteran general of the Hongwu era, unlike Sheng Yong, who had transitioned from a civil to a military post—he had fought his entire life and defended cities his entire life. Zhen Ding was well-supplied with provisions, and its moats were deep and wide; he was not afraid of a siege. But he also knew that Zhu Di, after defeating Jiahe, was heading straight for Zhen Ding, taking advantage of Sheng Yong's recent defeat and the unrecaptured Jinan, preventing him from joining forces with Sheng Yong.

"Order the entire army to go to the city," Wu Jie turned around, "and be on guard day and night without any slackening. Set up double the number of deer antlers outside the city, bury bamboo sticks in the moat, and prepare kerosene inside the city gate—not to guard against anything else, but to guard against the Yan army sending suicide soldiers to blow up the city gate."

Shen Du did not blow up the city gate. He had no intention of even approaching the city gate.

He stood in a reed bed on the north bank of the Hutuo River, with a newly built temporary weir at his feet. Zhao Laoliu, along with his engineers and auxiliary soldiers, had been piling up earth, stones, and sandbags on the old embankment, turning the Hutuo River, which was originally only two feet deep, into a deep pool. The river had been accumulating for a whole day under the control of the three weirs, and now the water level had risen to less than a foot from the top of the weirs, the water pressure causing the wooden piles of the weirs to tremble slightly.

"Release the water." Shen Du waved his arm.

Zhao Laoliu, along with his auxiliary soldiers, simultaneously breached the thinnest section of the dam, unleashing the pent-up waters of the Hutuo River, which roared forth and surged along the old riverbed towards the southwest corner of Zhengding City. The water level was low—less than two feet—but the current was extremely swift, carrying mud, sand, and gravel as it swept through the city. The deer antlers deployed by the Southern army outside the city were uprooted by the floodwaters, the bamboo spikes in the trenches were all submerged in the churning mud, more than a dozen of the outermost chevaux-de-frise were washed away, and the iron chains connecting the deer antlers could not withstand the water pressure and broke one after another.

"Now it's not just about destroying his antlers," Shen Du drew his sword, the blade pointing towards the southwest corner that had been swept away by the flood, "it's about completely shoveling up the outermost barrier of his moat."

The Southern army generals inside Zhen Ding City were stunned by the sudden flood. Wu Jie looked down from the city wall and saw his carefully arranged antler-shaped defensive formation washed away by the water, his face turning ashen. Zhu Di's cavalry had already taken advantage of the flood to rush in from the northwest—not to attack the city, but to attack the outer perimeter. Huo Zhen's mounted archers used the antler-less areas washed away by the water to leap over the base of the city wall, unleashing a volley of arrows that slammed onto the city walls, pinning the defenders behind the crenellations to their knees. Zhu Neng's central infantry followed closely behind, pushing battering rams with chassis reinforced by Shen Du, directly crushing the remnants of the flooded moat in the southwest corner.

The muskets on the southern city walls fired. However, after the water attack, the terrain outside Zhengding City was muddy, and the musketmen could not stand steadily. Several muskets exploded as mud and water splashed into the barrels. Wu Jie's deputy, Wang Bin, led a suicide squad out of the west gate to rescue the outer defenses, but they were cut off halfway by Zhu Neng's cavalry. Chen Mao led eight hundred fresh cavalrymen out from the flank, cleaving the flag in front of Wang Bin's horse in two with a single stroke. Wang Bin's troops were thrown into chaos and scattered in the mud.

The Yan army breached two city gates in quick succession, advancing directly towards the inner city. Wu Jie, atop the city wall, drew his sword and cut the ropes binding the commander's flag, preparing to die defending the city. However, his personal guards carried him down the ramparts and forcibly pushed him onto a warhorse heading south. The Zhen Ding garrison collapsed completely after losing its commander; some surrendered, others fled.

Shen Du walked in the procession entering the city, passing through the muddy breach in the city wall. Zhao Laoliu followed beside him, a pipe dangling from his lips, glancing at the remnants of deer antlers washed away by the flood, and twirling the pipe with satisfaction. Soldiers from the centurion's garrison followed behind, covered in mud. They were crossing this newly surrendered city, heading towards Zhu Di, who was unfolding the next military plan in the government office—His Highness was already summoning his generals to discuss the next strategy for the advance.