However, he said that after Tian Chengsi led the army to retreat to Yunzhou City, he handed over the defense of Yunzhou to his nephew Tian Yue, who was good at fighting, and he went to Fanyang to meet Emperor Shi Siming, tell him about the successes and failures of the Taiyuan Campaign, sum up the lessons and lessons, and not make the same mistake when he makes a comeback in the future.

As soon as he returned to Fanyang from Yunzhou, Li Siye had already led a large army to surround Yunzhou. Tian Yue lived up to his uncle's entrustment, patrolled the defense of the city wall every day, cleared the wall, and ordered people to strengthen the city defense overnight, and sent people to Fan Yang for help.

Li Siye ordered the besieging soldiers to organize troops to strictly investigate and intercept, and the messengers sent out by Yunzhou three times before and after were captured and imprisoned, these Tian Yue naturally did not know, he confidently believed that his uncle would soon bring a large army to rescue Yunzhou.

However, this time Li Siye was well prepared, and the 30,000 troops transferred from Guanzhong did not carry an artillery battalion because of the mountainous journey, but they carried many explosive bombs and fierce fire mines with amazing lethality, which could be thrown onto the city wall with improvised projectile weapons such as catapults and ballistas.

The hot air balloons he had worked on before were also made to improve the drawings, and the craftsmen could make more regular and perfect hot air balloons through the drawings. It only needs to be made with local materials and bamboo, wood and grease, which is a new tactical breakthrough from the ground to the air.

The usual trick of the defenders is to block the city gate with bricks, stones and mud tiles, so that even the most powerful battering ram cannot break the city gate, and can only obediently use siege equipment to climb the city wall.

Yunzhong and Daijun are the frontier positions of the Han Dynasty to attack the Xiongnu, and become the capital of the Northern Wei Dynasty, the city has been repaired by successive dynasties, and it has already been impregnable.

The fortifications of the city were extremely tight, not only with strong crossbows for long-range strikes, but also with sandalwood that could be used repeatedly, and the walls of the city walls were cleverly constructed like concave and convex shapes, so that the siege team could not help each other.

Li Siye estimated in his heart that if the traditional old method was used to attack the city, nearly 10,000 people would be lost on the city, and such a loss would be almost a fiasco.

He will never allow the lives of his soldiers to be wasted in the battle, and he must use a clever method, even if he spends more money and military expenses, and wastes more manpower and material resources, it is much better than consuming lives.

For this reason, he came up with a very simple and effective stupid method, that is, to use the tunnel to dig under the gate of Yunzhou City, and then use gunpowder to blow up the tunnel, and the city gate on the top and the bricks and stones blocking the city gate will fall below, so that he can successfully attack the city.

Facts have proved that Li Siye still wants to be simple, the military advisor Xu Bin used a hot air balloon to float into the sky to reconnoiter the structure of Yunzhou City, only to know that there are urn cities on all sides of Yunzhou City, it is not enough to blow up the city gate of the outer city, the city gate inside the urn city is the key, if Tian Yue really has the intention of defending, he will inevitably block the city gate of the inner city, so that the difficulty of the tunnel will increase infinitely.

Moreover, in terms of anti-tunnel warfare, the ancients also had very powerful soil methods, such as burying urns in the soil to listen to the sound of excavation underground, and after knowing the specific route of the enemy's tunnel, they could dig a large pit on the route they were digging to store water, and the enemy's excavation would inevitably be permeable.

Therefore, it must be a difficult thing to attack, and he expanded the besieging soldiers into thirteen excavation battalions, dug twenty-six tunnels into the city from four directions, and hired a special yin-yang arithmetic to determine the direction and distance.

Half of the tunnels were to be used to destroy the walls and gates, and the other half were to lead to remote areas of the city, where they were used to transport internal troops.

The entire tunnel operation took more than three months, during which Li Siye constantly sent people to use a catapult to throw explosive bombs and fierce fire mines into the city, causing a large number of casualties. Or they used hot air balloons to float over the city and drop bombs on the military camps and other places where they were densely populated, causing a strong panic in the city, and if this continued, many people were burned alive by the flames before the enemy could attack the city.

In order to avoid the bombs of the Tang army, the Yan army could only live in brick and wood buildings as much as possible, or dig cellars in the ground to live, and the soldiers on the city wall saw the hot air balloon floating in the sky, so they hurriedly beat the gong to convey the message, telling everyone to hide and not show their heads.

As the excavated tunnels were discovered by the enemy one by one, there were only six or seven tunnels available today, four of which were used to blow down the outer city gates, and two that led to the city of Urn City, and one that led to the houses in the city.

Some of these tunnels have shifted their orientation during the excavation process, and some have been dug too far or too close, and it is still unknown whether they will succeed. Li Siye ordered people to dig out a few more branches on the basis of the original tunnel, and bury and set up a few more explosion points in order to achieve the effect he imagined.

By the end of June, the sixteen newly dug passages had reached the preset length, just waiting to show their destructiveness.

On the morning of the 25th, he ordered people to use a coffin truck to carry explosive bombs and mines to the depths of the earth, and in order to achieve the best collapse effect after the explosion, the internal space at the end of the tunnel was dug wide enough

They transported the coffin to the preset location, leaving a rather long twist, and when everyone had withdrawn from the tunnel, they lit the fuse with torches.

On the ground, the Hexi army was already lined up, all kinds of ballistas and catapults for launching bombs were lined up neatly, and Li Siye rode his horse and waited with bated breath in front of Daxu, holding a pergola and looking at the Yunzhou city wall in the distance.

A rumbling sound sounded from underground, and the gate of Yunzhou City suddenly collapsed, and enthusiastic cheers came from the military array. Several explosions followed, and the walls collapsed in several places, but the effect was not ideal. Some of the walls had cracks in them, and although they looked precarious, they still stood firmly on the ground.

Tian Yue's face turned pale when he stood on the city wall, he had never seen such an attack, he once thought that the Hexi army was digging tunnels to attack the city from the ground, but he didn't expect it to be used to blow up the city wall.

"Quick! Hurry up and clean up the rubble! Block the gates! ”

Li Siye took out a horizontal knife from his waist, held it high in his hand and ordered: "Siege!" ”

In an instant, the ballista and the stone-throwing cart fired in unison, exploding sparks on the city wall, and the arrows that landed in the city gradually pierced the wall like a hedgehog's mane.

"Jumping Camp Charge!"

The soldiers held their shields and went towards the city gate, but before the Yan army had time to block the city gate with sandbags, the Hexi jumping camp had already poured into the city gate along the big pit that had been blown up.

But they successfully entered only the first gate of the collapsed party, the position of the inner urn city gate was blown off, although the wall collapsed out of a slope, but the Yan army condescended to fight desperately, and the Hexi army did not get the slightest advantage.

On another collapsed city wall, the two sides are fiercely fighting to the death, the Yan army mobilized the bed crossbow to the city walls on both sides, and the sharp arrows fired can easily penetrate the shield, the main attack of the Hedong army was suppressed for a while and suffered heavy losses, the Yan army continued to stab downward with spears, and the corpses of the Hedong army were covered with bricks and stones on the slope.

Dozens of hot air balloons rose into the sky, and they slowly flew over the city wall, and Yan Jun hurriedly propped up the bed crossbow and shot it back, piercing the hanging basket below. The sheepskin of a hot air balloon was pierced by a crossbow arrow, causing the balloon to tilt, and the flames tilted out of the copper furnace, instantly igniting the hot air balloon into a huge fireball and slowly falling to the ground, and the Hedong soldiers who were hit were unfortunately killed.

But they were helpless to reach the hot air balloon at the top of the wall, and the crossbow held by a single soldier did not pose much of a threat to it, and the bed crossbow could not be aimed vertically. Moreover, they had to take care of not only the threat in the sky, but also the enemy attack on the city walls.

The bombardier on the hot air balloon aimed at the bed crossbows and soldiers on the city wall, and threw them one after another, setting off fireballs and heat waves. The grease on the fierce fire thunder stuck to the armor and burned, turning the Yan soldiers into burning men, charging and slashing down in a frenzy, and the Hedong army lined up to pierce them.