Defensive tunnel.

It is a type of city fortification. Its purpose is to prevent enemy troops outside the city from digging tunnels underground to sneak past the city wall, and then launch attacks from within without anyone noticing.

Xiyun City originally 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 commander, from knowing the existence of this fortification.

Defense tunnels require extremely sophisticated design and construction. On the one hand, they need to support the thick soil layer above them so that they will not collapse when large troops pass by on the ground.

On the other hand, if the enemy accidentally digs out any of the supporting points when digging the tunnel, the entire defensive tunnel will have a chain reaction like dominoes and collapse, thus preventing the enemy from doing so.

The purpose of sneaking into the city from underground.

It is said to be a support point, but in fact it is not the obvious wooden piles, but the support points are integrated into the entire channel 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 accidentally destroys the mountain wall while digging the tunnel, it is very likely to cut through the middle.

support point, resulting in a chain reaction.

Needless to say, if a collapse occurs in the tunnel, it will cause serious consequences.

Especially in a large main city such as Bo'an City, a moat has been dug under the city wall. If the defensive tunnels further down the river were dug out, the river water weighing hundreds of tons would be smashed down, almost nothing could be done.

Possibility of survival.

As long as conditions permit, most general cities will dig such a defensive tunnel around their city. Over time, the generals responsible for siegeing the city will no longer choose to attack through tunnels, and these defensive tunnels will gradually be ignored.

If Chen Ze hadn't led the army to the side of the main city gate, Xu Qing and others had seen the rusty tunnel gate with their own eyes, and they would have probably forgotten that there was such a tunnel in Bo'an City.

Chen Ze brought his people here, of course he wanted to leave the city through the defensive tunnel.

This type of defensive tunnel actually has another name, called an escape tunnel.

Once the defenders are unable to withstand the powerful offensive from outside the city and it is a foregone conclusion that the city will be destroyed, the top brass in the city can rely on this passage to escape from the city and save their lives.

There is an exit to the outside of the city in the defensive tunnel. Not only is this exit extremely secretive, but there are also mechanisms inside the exit. People inside can go out, but people outside cannot enter through it. It is a one-way passage.

.

Xu Qing couldn't help but look worried when he saw that Chen Zezhen was planning to sneak out of the city through the defensive tunnel.

It is true that the tunnel can allow people to leave the city, but it is too narrow after all. It is true that a small number of people can pass through. However, for a large army of more than 30,000 people like them, the number is too large and the speed of passage is difficult.

It is bound to be slow, time-consuming and laborious.

Secondly, there are many people and many hands. This defensive tunnel has not been used for countless years. It is probably more fragile due to its disrepair. Xu Qing is afraid that if someone accidentally damages one of the supporting points, the moat above his head will be flooded.

If it is smashed down, it will be drowned if not killed on the spot. It is absolutely unlucky.

You must know that there are no drawings for this defensive tunnel. Only the craftsmen who built the tunnel knew about the entire layout and distribution of support points. But that was at least a hundred years ago. Moreover, even at that time, after Bo'an City built the tunnel, for defense purposes

The secret was leaked, and externally it was claimed that the craftsmen were being closely protected, but secretly who knew what was going on.

If Chen Ze gets his head in, it's very likely that he won't be able to get out.

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

He had come to see it once before and solved another problem that he was really worried about.

That's the problem with the air.

The tunnel is very narrow. If there is insufficient ventilation inside and too many people rush in at once, there is no guarantee that they will not die of suffocation.

And when he ordered someone to open the tunnel gate that time, the humid air that hit his face made him make a decision.

Being located at the bottom of a moat, humidity is inevitable, but the smell is very light. Not only that, but there is also a constant breeze coming out of the tunnel, which proves that there are many vents in the defensive tunnel.

Come to think of it, this passage is also responsible for providing an escape route for the city's high-rises. Naturally, it is impossible for the high-rises to suffocate to death in the tunnel.

That's why Chen Zecai led his troops here. Otherwise, he would have to go around the inner city gate of Bo'an and spend at least three more days climbing over the mountains and ridges through the gentle hills on the side.

That would achieve his plan, but the longer it takes, the less benefit he can get from it.

As for the problem that Xu Qing was worried about, there was no problem with Chen Ze.

After ordering someone to open the gate again, Chen Ze was silent for a moment, but he strengthened Cheng Yu's general star again in the system.

The battle merit of purchasing the general star fragments is naturally enough. With this breath, Chen Ze directly strengthened Cheng Yu until the duration soared to five hours, which was almost the same as Ma Teng before stopping.

Then he turned his eyes and smiled at Li Quan'an, who had just had a flash of purple in his eyes: "Then you will lead the way?"

"I obey!"

Li Quan'an responded with clasped fists, and without hesitation, he took the large backpack, small red flags and torches that had been prepared from the soldiers nearby, bowed slightly and entered the gate.

Chen Ze stayed outside for a while and coordinated the 30,000 soldiers behind him. Several of his close followers, including Gu Qingfeng and others who had just signed the accompanying documents, were all called together by him.

"Each of you will take a section, and you will be given strict instructions. Once you see such a small red flag in the tunnel, you must not touch the place marked by the red flag!"

He held several other red flags in his hand and distributed them to various people one by one. Then he personally led a team of sword and shield bearers and entered the gate with torches in hand.

Xu Qing and others looked at each other. It could be seen that Chen Ze was so confident and took the lead and went in by himself. They said nothing more and followed Chen Ze's instructions. They led the remaining 20,000 people separately and arranged them according to the queue.

Wait outside the gate and wait to get in.

As for Xu Qing's worry about the tunnel being accidentally destroyed, the key lies in that little red flag.

The person Chen Ze possessed Li Quan'an was naturally Cheng Yu's general.

One of Cheng Yu's three general skills is Insight, which is a powerful ability that can see through the enemy's ambush and weaknesses in advance.

When Cheng Yu first entered the tunnel, even though he didn't have a blueprint in his hand, he could still identify the hidden support points in the tunnel with his own ability.
Chapter completed!