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

The Yangtze River was just ahead. The Yan army marched south from the Huai River ferry for another six days. The further south they went, the hotter it became, and the heavier the humidity in the air. The veteran soldiers who had come from Hebei were beginning to feel the effects—not from the fighting, but from the climate. May had already brought summer, and the sun in Southern Zhili was scorching hot, making their armor unbearably hot. Sweat streamed down their armor, and after a day's march, their boots were soaked through. The wheat fields of the north had given way to paddy fields here, and the crisscrossing ditches and ponds fragmented their marching route, noticeably slowing the cavalry's pace.

Zhu Di entrusted the vanguard position to Zhu Neng, who placed Shen Du's centurion's unit at the very front of the vanguard. From Xuyi to Tianchang, and from Tianchang to Liuhe, Shen Du led his scout team southward, drawing topographical maps at each location, marking the positions of the southern army's outposts, the width of the rivers, and the number of boats available at the ferry crossings. His old injury in his left leg flared up repeatedly during the days of marching, making his limp increasingly noticeable. Zhao Laoliu noticed this but said nothing. Every day after setting up camp, he would quietly boil an extra pot of hot water and bring it to Shen Du's tent, placing the water bag beside Shen Du's legs before turning and leaving.

South of Liuhe, the terrain suddenly changed. The flat paddy fields and wetlands were replaced by rolling low mountains, not high, but steep, covered with dense, impenetrable pine and shrubbery. The official road wound its way through the valleys, its narrowest point only wide enough for two horses to walk side by side. Shen Du stood on a ridge, scanning the area southward with his binoculars. After putting them down, his expression turned grim. There were too many mountains. This terrain was unsuitable for cavalry deployment, for large armies to maneuver quickly, and even more unsuitable for the Yan army's preferred light cavalry flanking maneuvers. Yet, the Southern army excelled at ambushes in this kind of terrain—Sheng Yong had used similar terrain in Dongchang to trap Yan cavalry with hidden trenches and poisoned crossbows.

"What's this place called?" Shen Du asked the local guide beside him, a village chief in his fifties who had been brought in from Tianchang County. He was trembling with fear.

"Mount Qimei," the village chief pointed to the highest peak to the south, "that's the main peak of Mount Qimei. To the east is a small river, and to the west is—"

Shen Du didn't listen any further. He squatted down and used his dagger to draw a mountain range in the mud, circling the main peak of Qimei Mountain in the middle. Then he drew several horizontal lines around the main peak—those were the ridges and valleys. He stuck the dagger into the south side of the main peak: "This is where Your Highness wants to attack." He looked up at the southern horizon, where the outline of the main peak of Qimei Mountain could be vaguely seen, slightly distorted in the afternoon heat.

Zhu Di was indeed aiming for Qimei Mountain. After bypassing Jinan and advancing directly into the Jianghuai region, his objective remained clear: to capture a crossing point on the north bank of the Yangtze River, and then cross the river to besiege Nanjing. However, Xu Huizu arrived even faster than he anticipated. Jianwen urgently dispatched Duke Wei, Xu Huizu, from Nanjing to lead the elite central army north to reinforce the area. Xu Huizu did not take the Grand Canal, but instead crossed the river directly from Nanjing, passing through Pukou, Chuzhou, and Dingyuan, arriving at Qimei Mountain in three days. He brought with him 30,000 of the most elite infantrymen from the Beijing garrison and 5,000 musketeers from the Shenji Battalion, along with the troops of He Fu and Ping An already deployed around Qimei Mountain. The Southern army amassed nearly 100,000 troops around Qimei Mountain, establishing three lines of defense along the mountain ridge and valleys.

Xu Huizu's command flag was planted on the main peak of Qimei Mountain. He stood atop the mountain, watching the smoke from the Yan army's cooking fires rise from the valley to the north, his face calm and composed. He was Xu Da's eldest son, the hereditary Duke of Wei, and had grown up in the military camp since childhood, well-versed in military strategy and having seen bloodshed. Unlike his father, who had spent his life fighting on the offensive, his forte was defense—using the mountains and passes to trap the enemy in narrow tunnels outside fortified cities.

"The Yan army has come from afar, suffering from the unfamiliar climate and lack of supplies," Xu Huizu said to He Fu, his voice calm and unhurried. "Zhu Di wants a quick victory, but we will not fight him quickly. We will hold the pass, hold off his vanguard, and let the heat and hunger help us win." He Fu nodded, while Ping An stood aside, his hand on the hilt of his sword, saying nothing.

The Yan army began its attack on the Xiahe Pass on the afternoon of May 13th. Xiahe was a north-south valley on the western side of Mount Qimei, with very shallow water and banks lined with pebbles and shrubs. The narrowest point of the pass was only seven or eight zhang (approximately 33-40 meters) wide, and the mountainside on both sides was covered with dense, impenetrable pine trees. Shen Du had harbored doubts about this pass before launching the attack—topographically, it was a perfect ambush site. Troops could be hidden on the mountainside, and the open riverbed in front of the pass would completely expose the attackers to crossbow fire from both sides once they entered the riverbed. If he were in the Southern army, he would have deployed muskets on the mountainside, laid tripwires on the riverbed, and hidden reserves behind the pass for a counter-attack.

But he had no way to bypass it. He had traversed all the valleys surrounding Qimei Mountain, and every road was blocked by the Southern Army. Xiaohe Pass was the only way to the main peak of Qimei Mountain. Without taking the pass, he could not threaten Xu Huizu's main position; without threatening the main position, he could not drive the Southern Army away from Qimei Mountain; without driving away the Southern Army, the Yan Army could not continue south.

Zhu Neng led three thousand infantrymen in a frontal assault at the Xiaohe Pass. Shen Du's centurion unit was tasked with flanking from the eastern mountainside, aiming to eliminate the musket positions on the eastern side of the pass. Zhao Laoliu, carrying a bundle of miniature gunpowder canisters, led the way, a lit pipe dangling from his mouth, his steps light yet steady. Shen Du, leaning on his sword, walked in the middle of the column. His old left leg injury caused him pain during the climb, forcing him to stop and catch his breath every few steps, but he did not fall behind.

As Shen Du had predicted, the musket positions on the eastern hillside were indeed as they appeared—over two hundred Shenji Battalion musketeers crouched behind pine trees, their muskets mounted on makeshift stone walls, muzzles pointed towards the stream below the pass. From their position, every corner of the pass was within their firing range. Shen Du lay prone behind a rock and drew several lines on it with his dagger—a shallow ditch, overgrown with ferns, separated their hiding place from the musket positions; they could use it as cover to sneak across.

"Zhao Laoliu," Shen Du said in a low voice, "lead your men into the ditch, stuff the gunpowder canisters under the stone wall, and after they explode, don't linger. Retreat and fire arrows from the side. Gu Zhang, once Zhao Laoliu has blown open the stone wall, you lead the swordsmen and shieldmen to charge in from the front and block the breach. Zheng Biao, you lead the spearmen behind the swordsmen and shieldmen, using your spears to poke through the gaps in the shields, so the musketeers don't have time to reload."

Everyone was waiting for his final instructions. Shen Du took a step forward, and as soon as his left foot stepped into the shallow ditch, the mud beneath his foot suddenly slid down with a few pebbles. He glanced down at the water at the bottom of the ditch—a very thin film of oil floated on the surface, shimmering with iridescent colors in the midday sun.

"Stop—" Shen Du shouted in a low voice, but it was too late.

Suddenly, a burst of light appeared on the Southern army's musket position. Not muskets—but rockets. Dozens of rockets, each with a gunpowder cartridge, shot out from behind the stone wall, their shafts tracing arcs through the air, trailing white smoke, before embedding themselves in the crevices of the rocks in the stream and ditch, exploding with a deafening roar. These rockets were modified Southern army weapons; their arrowheads were tied with hemp rolls soaked in potent oil, so they wouldn't extinguish immediately upon landing, but instead spill the oil onto the rocks and water, continuing to burn. The oil film in the ditch ignited. Flames spread like snakes along the puddles, turning the entire ditch into a fiery trench. Zhao Laoliu was forced back several steps by the flames, his armor burned with several holes by the flying sparks. Zheng Biao was struck on the forehead by a flying piece of rock; blood trickled down his brow. He wiped it with the back of his hand, but didn't retreat.

Xu Huizu had already laid out his plans. He not only positioned muskets on the mountainside but also poured oil into the shallow ditch below, covering it with gravel, intending to set it ablaze once the Yan army reached the ditch. Zhu Neng's frontal charge was also suppressed by the muskets on the streambank. The narrowest point of the pass was blocked by the Southern army's chevaux-de-frise and tripwires, preventing the battering rams from advancing and the cavalry from maneuvering. The Yan army fought their way from the Xiaohe Pass to the foot of the main peak of Qimei Mountain, engaging in fierce fighting from noon until dusk. They launched six repeated charges in three hours, all of which were repelled. When the casualty figures were tallied at dusk, Zhu Neng slammed the military report to the ground—three thousand men had been lost, two commanders killed in action, one deputy commander seriously wounded, and the three youngest recruits in the Shen Du Hundred-Household Garrison had failed to retreat from the shallow ditch.

This was the first real defeat for the Yan army since the victory at Jiahe.

At night, the Yan army retreated to the northern valley and set up camp. The campfires burned dimly, and no one spoke, only the sound of sharpening knives echoed throughout the room. Zhu Neng sat on a rock, his old wound on his right arm reopened, and the army medic squatted beside him, changing his bandages. He grimaced in pain but didn't utter a sound. Chen Mao stood not far away, sharpening his knife for half an hour and still continuing. Huo Zhen leaned against his saddle, slowly whittling at another horse bone with his dagger.

For the first time, the idea of ​​retreating was raised in the central command tent.

"Your Highness, the terrain of Qimei Mountain is extremely unfavorable to our army. The valleys are narrow, making it difficult for our cavalry to maneuver, and the musket formations are too dense. A direct charge would only result in casualties." An elderly commander with gray hair stood up, cupped his hands, and spoke in a heavy tone. "Moreover, the weather is getting hotter and hotter, and diarrhea and fever are already spreading in the army. Our food supplies are also running low. It would be better to retreat to the north bank of the Huai River to rest and reorganize, and then discuss marching south again after the weather cools down in autumn."

Zhu Neng suddenly stood up, his right arm still bandaged, and slammed his fist on the table: "Retreat? Retreat what?! We fought our way from Dezhou to the Yangtze River, and now retreating to Huaibei would mean all our efforts were for nothing! How can we face the brothers who died at the foot of Qimei Mountain?"

"Are we going to keep throwing lives into the pass instead of retreating?"

"you--"

"Silence, all of you," Zhu Di said. He sat behind his desk, a topographical map of Mount Qimei spread out in front of him, covered with dense corrections in vermilion ink. His expression was unreadable in the candlelight, but his voice was hoarse—days of marching and the summer heat had swollen his throat so much that he could barely speak, and every word he uttered sounded as if it had been sanded.

"The Qimei Mountain pass is too narrow; we can't break through head-on." His finger lingered on the location of the main peak of Qimei Mountain on the map for a long time, then slowly moved westward to a mountainous area deeper upstream of the stream. "Xu Huizu has concentrated his forces on the front; there must be weaknesses elsewhere. Keep an eye on Qimei Mountain, send out all available scouts, and find the weak points in his forces, no matter what method we use."

Shen Du stood at the tent entrance, leaning against a tent post, his left leg aching so much that he shifted all his weight onto his right. He had retraced his steps through the nearby mountains after dark—he hadn't even had time to remove his armor upon returning; the plates were covered in grass clippings and dirt. He looked up at the flickering candlelight inside the tent.

The next day, before the scouts could report back, news arrived from the Southern army's positions—not of an attack, but of a retreat. Xu Huizu had withdrawn.

The Jianwen Emperor issued an edict from Nanjing, urgently summoning Xu Huizu to lead his troops back to the capital. The edict was stern and left no room for argument—"The defenses of the capital are weak. Duke Wei must immediately lead his troops back to defend the capital without delay." The court officials in Nanjing panicked upon hearing that the Yan army had reached Qimei Mountain, less than a hundred li from the Yangtze River. They feared that Zhu Di would bypass Qimei Mountain and cross the river directly, that Nanjing lacked sufficient troops to defend the city, that Xu Huizu could not hold out at Qimei Mountain—and even more so, that Xu Huizu would be holding onto his troops outside the city. Various impeachments and secret memorials poured into Jianwen's court from the Five Military Commissions and the Six Ministries. Some said, "I fear Xu Huizu is becoming too powerful," others said, "The capital is in imminent danger; only Duke Wei can defend it," and still others suggested, "It would be better to recall Xu Huizu to guard the river."

Jianwen believed it. Or rather, he had no choice but to believe it. He was still too young, born and raised in the inner palace, tended by women, with everyone around him telling him in various ways how dangerous the outside world was. He didn't know what was happening at the front, how long the defenses at Qimei Mountain could hold out, or how long Xu Huizu's forces could hold off the Yan army. He only knew that Nanjing's walls were high, but its garrison was small. So, on a sleepless night, he summoned Qi Tai, the Minister of War, and drafted an edict to recall Xu Huizu overnight, which was sent out by fast horse at dawn.

When Xu Huizu received the imperial edict, he was on the main peak of Qimei Mountain, deploying defenses for the day. He read the edict three times, then folded it and tucked it into his robes, his face expressionless. He stood on the summit, gazing at the Yan army's camp to the north, for a long time. He had taken all 30,000 of his most elite infantry and 5,000 musketeers back to Nanjing, leaving only He Fu and Ping An's exhausted troops to hold the line at the Qimei Mountain front.

Shen Du stood on the ridge, watching through binoculars the Southern Army's troops dismantling their camps. He saw Xu Huizu's command flag slowly lowered, the Southern Army's orderly ranks moving south, and the once dense array of banners on the main peak of Qimei Mountain disappearing one after another. He lowered his binoculars, remained silent for a long while, then turned to Zhao Laoliu and said something.

"Report back to Your Highness—Xu Huizu has withdrawn."