Cao Cao retreated to Guandu with a large army, with only 50,000 troops in his hands.

Zhao Hui repaired in Yanjin for two days, and the army began to march towards Guandu.

Along the way, countless spies ploughed the court and swept the caves to prevent Cao Jun from ambushing.

Yanjin pursued, Cao Cao suffered heavy losses, and Zhao Hui also lost nearly 20,000 people.

Can't be careless.

Along the way, the plough court swept the caves, although Cao Cao's ambush was not found, but Cao Cao's more than a dozen waves of spies were destroyed.

The Cao army of Guandu has strengthened the city wall again in the past few days.

But everyone's face is very solemn.

Man Zhong was sent back to Xudu by Cao Cao to continue recruiting an army.

In addition, Cao Ren went to Yuzhou, and Cao Cao prepared to transfer the soldiers left behind in Yuzhou, as well as Xiahoudun of Xudu, to Guandu.

As for the emptiness of the rear forces, Cao Cao can't care about it now.

Sun Ce, who was the most threatening, was now injured and returned to Huiji County. Let Cao Cao dare to make this determination.

If Guandu is lost, the line from Guandu to Xudu is almost a flat river, and Cao Cao will be even more unable to resist Zhao Hui.

Liu Biao, Zhang Xiu, and Lu Bu are all unstable factors, but Cao Cao really doesn't have the energy to take care of them now.

I can only go all out, break the cauldron and sink the boat, and concentrate all the soldiers and horses in Guandu.

Zhao Hui led a large army to attack the city every day.

However, on the side of Guandu, after Cao Cao's reinforcement many times, it became more and more difficult to overcome, and the city wall was one zhang thick and more than two zhang high.

In addition, the walls protrude outward, making it difficult to climb with rope ladders.

And the city gate is now directly sealed by Cao Cao with stones from the inside.

Even if Zhao Hui uses siege vehicles, he can't open the city gate now.

If you want to break the city, you can only climb the city wall.

However, if you kick the wall and attack, the casualties will be very large for the Zhao army.

It is very likely that he failed to capture Guandu, but gave Cao Cao a chance.

With Guandu's current defense, if it is attacked, the casualty ratio will be at least three to one.

On Zhao Hui's side, the lives of three soldiers can be exchanged for the lives of one Cao Jun.

If it is only three to one, with the current army in Zhao Hui's hands, it can barely attack Xiaguandu.

But if the casualty ratio rises to five to one, the current hundreds of thousands of troops in Zhao Hui's hands will not be enough.

Not to mention that Cao Cao transferred the last army from Yuzhou, the capital of Xu.

Even the 50,000 Cao troops here in Guandu can fight Zhao Hui's 150,000 troops.

The weather has been very good these days, and Zhao Hui personally leads the army to feint every day.

wants to lure Cao Cao out.

However, Yanjin was lured once by Zhao Hui in danger, and Cao Cao, who suffered heavy losses, now completely ignores Zhao Hui.

Even if Zhao Hui came to the city gate in person, Cao Cao was indifferent, but stood on the city wall, laughing with Zhao Hui, showing his optimistic attitude, even at this time, Cao Cao was not depressed.

Because Cao Cao relaxed and optimistic, the morale of the Cao army in the city did not decline all the time.

"Lord, the city here in Guandu has thick walls, do you want to order someone to dig a tunnel to enter?" Xu Yu came up with a plan.

It takes ten days and a half months to dig a tunnel, and one tunnel is definitely not enough, more than a dozen tunnels need to be dug together.

Zhao Hui thought for a while, shook his head and said: "Digging the tunnel, it is easy to be discovered, and the soldiers in the tunnel will be buried alive at that time." ”

"Lord, although the tunnel may be discovered by Cao Cao, it is also possible that Cao Cao will not be able to find it." Xu Youdao.

There was another sentence in his heart, which he didn't say: even if Cao Cao found out, it would only bury hundreds or thousands of people. In a war, there are so many more people killed.

"Lord, what Ziyuan said is right, although it may be discovered, but now the official crossing is difficult to break, this is also a method, it is still worth a try." Guo Jiadao.

Whether Cao Cao will find out or not, there is no absolute.

As long as they are careful, they will send the excavated soil to a farther place so that Cao Jun cannot see it. There is still a high possibility of hiding from the world.

Zhao Hui remembered that Yuan Shao and Cao Cao fought in Guandu, and it seemed that they had also dug tunnels, but they were discovered by Cao Cao.

But now that Guo Jia said the same, Zhao Hui agreed to give it a try.

If you want to defeat Guandu, now in addition to attacking, it seems that there is really not much way, if you don't dig a tunnel, you can only spend time with Cao Cao.

Wei Shuang had already taken thirty warships to the South China Sea to transport a large amount of grain from Jiaozhou.

Although Zhao Hui's 150,000 troops are concentrated here, Zhao Hui's grain and grass are still sufficient, even if Wei Shuang does not come back, the current grain is enough for Zhao Hui to support a year.

But how long can the grain and grass in Cao Cao's hands last?

Zhao Hui still doesn't know that Zhao Hui's spies haven't been able to inquire about Cao Cao's specific amount of grain and grass yet.

It is certain that there are fewer soldiers and horses than Zhao Hui, but Cao Cao also has fewer soldiers and horses.

The daily consumption of grain and grass on Zhao Hui's side is at least five times that of Cao Jun.

Not only because of the difference in the number of soldiers, but also because of the food conditions of Zhao Jun, which are better than Cao Jun.

If you add the distance of grain and grass from Youzhou and Jizhou, the consumption will be even greater.

Zhao Hui now has an army of 150,000 in his hands, and the consumption of grain and grass every month is about 150,000 stones, which is almost 2 million a year.

Coupled with the consumption of transportation, if this war is really fought for a year, Zhao Hui needs to burn four million stones of grain and grass.

And Cao Cao only needs to prepare a million stones.

The more time passes, the greater Zhao Hui's consumption will be.

If Cao Cao can really hold out for a year, Zhao Hui will be dragged down, and after the army withdraws, it will take at least two more years.

"Okay, dig a tunnel, it's okay if it's far away, you must keep it secret, don't be discovered by Cao Jun." Zhao Hui said.

Although Cao Cao sealed the city gates, Cao Cao's army still went out of the city every day. They were on the city wall and slipped down the hanging ropes.

When they returned, someone would naturally throw the rope down and pull them up.

Although trapped in Guandu, Cao Cao would send people outside the city every day to collect information about the Zhao army.

Know yourself and know your opponent, and you will not be defeated in a hundred battles.

No matter how bad the situation is, Cao Cao will not let his eyes be blindfolded.

Even if half of the spies sent out every day could not come back, Cao Cao still insisted.

A thousand Zhao troops left the camp and went to the east of Guandu, where there was a piece of woodland, less than five miles away from the city of Guandu.

1,000 people, divided into five teams, each team of 200 people, prepared to dig a total of five tunnels.

First, a large pit with a width of ten zhang was dug, and then five tunnels were divided, distributed along the fan-shape, and dug towards the side of Guandu.

To the north of Guandu, there were also a thousand people.

Zhao Hui was ready to dig a total of ten tunnels.

The excavated soil is only removed at night.

Pull into the mountains ten miles away.

Then around the tunnel, Zhao Hui arranged several patrol teams.

They didn't get too close, and the patrol routes were different, that is, more than a dozen patrol teams, along different paths, but every quarter of an hour, a team would pass by this side.

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