Defensively authentic.

It is one of the fortifications of the city, the purpose is to prevent the enemy outside the city from sneaking over the city wall by digging tunnels, and then attacking from the inside unconsciously.

At first, West Cloud City wanted to dig a defensive tunnel, but after discovering that there was a layer of hard rock under the city wall, it gave up this plan.

But this does not prevent Xu Qing, the former city defense captain, from knowing the existence of this fortification.

The defensive tunnel requires very sophisticated design and construction. On the one hand, it needs to support the thick soil layer above so that it will not collapse when a large force passes by on the ground.

On the other hand, when the enemy is digging the tunnel, as long as any one of the support points is accidentally digged, the entire defensive tunnel will have a chain reaction like dominoes, and then collapse and stop the enemy. The purpose of sneaking into the city from underground.

It is said that it is a support point, but in fact it is not the kind of obvious wooden piles, but the support point is integrated into the entire passage in a very clever way by skilled craftsmen.

There may be at least three to five such support points hidden in the mountain walls on both sides of a passage of about a hundred steps. As long as the enemy forces accidentally damage the mountain wall while digging a tunnel, it is very likely to smash the middle. Support point, and even have a chain reaction.

If there is a collapse in the tunnel, the serious consequences it can cause need not be said.

Especially in major cities such as Bo'an City, a moat has been dug under the city wall. If the defensive tunnel below the river bottom is dug off, the river water weighing several hundred tons will fall down. The possibility of survival.

As long as conditions permit, most of the general cities will dig such a defensive tunnel around their own city. Over time, the generals in charge of the siege will no longer choose to attack in an authentic way, and these defensive tunnels will gradually be ignored.

Had it not been for Chen Ze to walk to the side of the main city gate, Xu Qing and others had seen the already rusty tunnel gate with their own eyes, and they would have forgotten that there is such a tunnel in Bo'an City.

Chen Ze brought people here, of course he wanted to get out of the city through a defensive tunnel.

This kind of defensive tunnel actually has another name, called escape route.

Once the defender can't resist the powerful offensive outside the city, when the city will be broken, it is a foregone conclusion, the high level inside the city can rely on this passage to escape outside the city and save their lives.

There is an exit to the outside of the city in the defensive tunnel. This exit is not only built to be extremely secretive, but also has organs inside the exit. People inside can go out, but people outside cannot enter through it. It is a one-way passage. .

Seeing that Chen Ze really planned to sneak out of the city from the defensive tunnel, Xu Qing couldn't help but look worried.

It’s not fake that tunnels can accommodate people out of the city, but after all, it’s too narrow to allow a small number of people to pass through. But like them, large troops with more than 30,000 people, there are too many, and the speed of passage It is bound to be slow, time-consuming and laborious.

Secondly, there are too many people and hands. This defensive tunnel has not been used for many years. It may be even more vulnerable when it is in disrepair for a long time. Xu Qing is afraid that if someone accidentally damages one of the supporting points, the moat above his head. If you smash it down, you will have to drown if you don’t get smashed to death on the spot. It is absolutely unreasonable.

You must know that this defensive tunnel has no drawings. The entire layout and the distribution of supporting points are only known to the craftsmen who built the tunnel back then, but that was at least a hundred years ago. Moreover, even at that time, after the tunnel was repaired in Boan City, it was for defense. The secret was leaked, and it was claimed to the outside world that those craftsmen were tightly protected, but secretly, who knew what was going on.

Chen Ze's head got in, and it is very likely that he won't get out.

This is Xu Qing's concern, but it is not within Chen Ze's consideration.

He visited it once before and solved another problem that he was really worried about.

That is the problem of air.

The tunnel is very narrow, and if there is insufficient ventilation inside, if too many people swarm in here, it is impossible to guarantee that there will be no suffocation problem.

And when he ordered someone to open the tunnel gate that time, the damp air rushing toward his face made him judge.

Located at the bottom of the moat, humidity is inevitable, but the smell is very light, not only that, but there is also a continuous breeze gushing out of the tunnel, which proves that this defensive tunnel also has many vents.

Think about it, this channel also shoulders the important task of providing escape channels for the high-levels in the city, and it is naturally impossible to let the high-levels suffocate in the tunnel.

That's why Chen Ze led the troops here. Otherwise, he would have to go around the inner city gate of Bo'an, and it would take at least three more days to climb over the mountains from the low side of the mountain.

That way he can achieve his plan, but the longer the delay, the less he can benefit from it.

As for Xu Qing's concerns, there is no problem with Chen Ze.

After ordering people to open the gate again, Chen Ze was silent for a while, but Cheng Yu's General Star was strengthened again in the system.

Naturally, it was enough to purchase the battle exploits of Star Shards. With this breath, Chen Ze directly strengthened Cheng Yu until the duration soared to five hours, almost equal to Ma Teng before stopping.

Immediately he turned his eyes, and Li Quanan, who had just flashed a touch of purple under his eyes, smiled and said, "Then you will lead the way?"

"The minister obeys!"

Li Quanan answered with his fists, without hesitation, the soldier next to him took the small red flag and torch that had been prepared a long time ago, and he bowed slightly and entered the gate.

Chen Ze stayed outside for a while, and organized the 30,000 soldiers behind him. Several of his confidants, including Gu Qingfeng, who had just signed his entourage, were called together by him.

"You will receive a section each, and you will emphatically order to continue. Once you see such a small red flag in the tunnel, you must never touch the place marked by the red flag!"

He held several other red flags in his hand and distributed them one by one to the hands of various people. Only then did he personally lead a group of swordsmen and shields, and also entered the gate with torches.

Xu Qing and the others looked at each other. It can be seen that Chen Ze was so confident and the first soldiers went in by themselves. They stopped saying anything. According to Chen Ze's instructions, the remaining 20,000 people were led separately and in line. Wait outside the gate and wait to get in.

As for Xu Qing's worrying tunnel, in case it is accidentally destroyed, the key lies in the little red flag.

Chen Ze possessed Li Quanan, naturally Cheng Yu's general.

One of Cheng Yu's three general skills is an opportunity for insight, which is a powerful ability that can see through the enemy's ambush and weakness in advance.

From Cheng Yu advanced to the tunnel, even if he didn't have a blueprint in his hand, he could still distinguish the hidden support points in the tunnel with his own ability.

A small red flag was inserted when they found one. As long as the people behind did not touch it, they would not damage the support point, and naturally there would be no danger of collapsing.