Although Tan Shihuai told Li Ru about the plan to send a small group of people to infiltrate the Han territory to cause sabotage, he did not reveal the number of people to be sent or the specific location.

After bidding farewell to Tan Shihuai, Li Ru returned to his residence, then took out a map of the Great Han's defenses and began to ponder the possible locations Tan Shihuai might attack.

Unfortunately, despite pondering for a long time, Li Ru was unable to figure out the location that Tan Shihuai intended to destroy.

In the past few years, Zhang Huan, who was stationed in Bingzhou, and Lu Zhi, who was stationed in Youzhou, have been busy reinforcing and repairing the Great Wall defense line, in addition to organizing and training their troops.

Today, the Great Wall from Youzhou to Bingzhou has been completely repaired. Even in some dangerous areas, defensive fortresses and beacon towers have been built using concrete.

Moreover, there were nearly 200,000 guards patrolling the Great Wall defense line between You and Bing.

In Li Ru's vision, it would be virtually impossible for Tan Shihuai's cavalry to bypass the Great Wall and enter the territory of the Han Dynasty; even a small force would not have an easy time.

However, thinking of Tan Shihuai's confident demeanor, Li Ru frowned even more deeply.

"Could it be that he has access to a small path leading into the territory of the Han Dynasty?"

Looking at the near-perfect defensive map of the Han Dynasty, Li Ru couldn't help but murmur aloud.

This seems to be the most reasonable explanation, and the route is not obvious, so only small groups can travel along it.

With this in mind, Li Ru turned his gaze to the mountains in Yunzhong, Wuyuan, Shuofang, Shanggu, Daijun and other places.

With Huangfu Song and the Bingzhou Grand Camp in Wuyuan and Shuofang, it was difficult for the Xianbei people to achieve anything.

The northern part of Dai County was the territory of the Yuwen tribe, and the northern part of Shanggu was the territory of the Red Ribbon Army.

Tan Shihuai could only choose between Yunzhong or Dingxiang.

But between those two counties, the mountains and forests are dense and the terrain is complex. Finding such a small path is not so easy.

Even if I send a message to the Han Dynasty and ask the officials of the two prefectures to search, by the time they find them, the people from Tan Shihuai's faction will probably have already infiltrated the territory of the Han Dynasty.

"Yunzhong, Dingxiang..."

Softly murmuring the names of the two prefectures, Li Ru finally set his gaze on Yunzhong Prefecture.

Previously, I had suggested that Tan Shihuai go to Yunzhong to set up a feint, but Tan Shihuai immediately proposed a plan to harass them.

Clearly, Yunzhong County is where the secret passage is located.

Nevertheless, Li Ru still dared not make a decision easily.

It's better to be safe than sorry. If we misjudge and send out the message too easily, not only will the soldiers guarding the border have worked in vain, but it will also buy more time for the Xianbei people who have infiltrated the Han Dynasty.

Li Ru absolutely could not accept this outcome.

After thinking for a long time, Li Ru put away the map on the table, then got up and walked towards the royal library.

With the assistance of Li Ru, Han Sui, and a group of Han strategists, the present-day Danhanshan Royal City, with its outer city walls and inner outer city, even its layout bears a resemblance to the Han Dynasty.

Moreover, Tan Shihuai followed the example of the Han Dynasty, not only setting up various government offices in the city, but also building a library in the palace to store books looted from the Han Dynasty and various correspondence.

In the words of Tan Shihuai, the Xianbei should also have their own history, just like the Han Dynasty.

Li Ru went there hoping to find some clues in the library.

Li Ru guessed that the small path leading to the Han Dynasty that Tan Shihuai controlled must have been a smuggling route in the past.

With the powerful local strongmen in the border regions being forcefully wiped out by the emperor a few years ago, this smuggling route was abandoned and has remained undiscovered to this day.

Before long, Li Ru entered the palace and arrived at the library with a token given to him by Tan Shihuai.

When the soldiers on duty saw that it was Li Ru, they quickly bowed respectfully and let him in without asking any questions.

After entering the library, Li Ru went straight to the area in the stadium where correspondence was stored.

Soon, Li Ru arrived at a row of wooden shelves, where more than twenty parchment scrolls were neatly arranged.

Li Ru casually picked up a parchment scroll, opened it, and saw that it was written in Sanskrit.

Li Ru also had some knowledge of Sanskrit. He glanced at the contents and then shook his head.

The parchment scroll contained only information about some Western Region countries, which was of no help to Li Ru at this time.

After rerolling the parchment and putting it back in its place, Li Ru picked up the second parchment.

Upon opening it, it was still in Sanskrit, but this time the content was different. It mentioned horses, refined iron, salt, grain, and other items, so it seemed to be about a trade.

Although the text did not mention which country the transaction was with, Li Ru immediately thought of the Wusun Kingdom.

After memorizing the contents, Li Ru reached for the third parchment scroll, the contents of which were also in Sanskrit…

It wasn't until he opened the ninth page and saw the Chinese characters on it that Li Ru's previously composed expression relaxed somewhat.

The inscription read: "One hundred shi of salt requires three hundred taels of gold; one thousand jin of refined iron requires seven hundred taels of gold. Upon leaving Yunzhong, the money and goods were settled."

Upon seeing the words "in the clouds" above, Li Ru's lips curled slightly.

As he had guessed, the secret passage that Tan Shihuai possessed was indeed in the clouds.

Unfortunately, the specific location was not specified in the parchment scroll.

After carefully putting the sheepskin roll away and returning it to its original place, Li Ru took down another sheepskin.

The following parchment scrolls were all written in Chinese characters, and their contents were all about trade. In addition to goods such as grain, salt, wine, and silk, they also included armor and weapons.

Li Ru didn't bother to remember these things. He knew that the later items were all defective products that the emperor had arranged to be sold to Tan Shihuai.

After a long time, only one parchment remained unread on the wooden shelf.

"Sigh!"

After sighing, Li Ru still held a glimmer of hope and reached out to take the last parchment scroll.

Just as Li Ru opened the parchment scroll and had not yet had a chance to look at it, he suddenly heard footsteps behind him.

Li Ru straightened up and immediately focused his gaze on the parchment scroll, feigning complete concentration.

"Mr. Wen, what are you looking at?" Tan Shihuai's voice reached Li Ru's ears.

Li Ru looked up with an "Ah!" and then turned around, only to see Tan Shihuai smiling at him.

Li Ru quickly bowed and said, "Greetings, Your Majesty!"

Tan Shihuai smiled and waved his hand, "Sir, you don't need to be so polite. I just sent someone to look for you, and they said you came here, so I came to see you!"

Li Ru nodded slightly: "I was just browsing around when I had nothing else to do, and when I saw these things, I decided to take a look!"

Tan Shihuai hummed in agreement and turned his gaze to the parchment scroll in Li Ru's hand.

"Huh? Mr. Wen, do you perhaps recognize the characters on this picture?"

Upon seeing the map on the parchment scroll, Tan Shihuai couldn't help but let out a soft exclamation and looked at Li Ru with a curious expression.