No matter how the follow-up campaign is to be fought, the idea of "keeping secrets, dividing troops and advancing slowly, and fully investigating" in the first stage is always correct.

So after discussing it with Li Su, starting the next day, Liu Beijun began to go south in batches one by one, consolidating the transit base while exploring the road, and transporting and hoarding grain and grass.

It took three days for the army to be divided with Huangfu Song on the twenty-ninth day of the first month, and the thirtieth army of the first month went out of the pass, and it took three days to raise the head of the second dragon in early February.

The day when the dragon raised its head, in terms of solar terms, was about a few days after the sting, so when the army turned over the main ridge of the Qinling Mountains, the snow in the valley had almost melted, and the peak next to it was still not finished.

The valley is already very muddy, and you can often see a trickle of water flowing down the valley. Seventy or eighty miles southwest from Sanguan, all the way to the East Wolf Valley, the terrain gradually becomes higher, so these snowmelt water will continue to flow in the direction of Chencang City.

Li Su rode on horseback for most of the journey and enjoyed the highest civil treatment, but when he encountered a dangerous place that was really muddy and unstable, he could only dismount and be supported by the samurai.

When they walked to the East Wolf Valley, the army rested temporarily, and Liu Bei found Li Su, ate some dry food and wine together, and talked by the way.

Liu Bei personally broke a piece of donkey meat and burned it to him, and sighed: "I have been living in Shuofang for a long time, the difficulty of this Shu Road is only an eye-opener today, no wonder Zhang Lu can intercept and kill the Han envoy." Walking on Chencang Road is already so muddy, if you take the Baochuan Road in Yixian County, or even directly into the meridian road of Chang'an, I don't know how dangerous it is. ”

Li Su took a sip of water before taking the fire: "It's just muddy, it's okay to solve it, just wait for the snow melt and water to flow out." It is precisely because of this that the mud and snow have just melted away, and our army's advance is sudden, and Zhang Lu is easy not to be on guard, which is worth suffering. ”

Liu Bei threw a small pebble into the mountain stream, shook his head and sighed: "If you don't take precautions, there won't be a single patrol post on Yangping, let's sneak up on the wall, right?" As long as you start to tackle the key problems, you can't take it for a moment, and the enemy reinforcements are not coming in a steady stream. ”

Li Su didn't want to say frustrating words, so he wanted to find a topic crooked, he looked at the splash of the pebbles thrown by Liu Bei in the mountain stream, his heart moved, and asked:

"Are there any local business travelers and medicine farmers who have been detained to the north today? I was trying to ask the natives who were familiar with geography to ask, can the meltwater of the snow in the mountains really flow under the city of Chencang? When we set out from Chencang, there was no river flowing out of the Qinling Mountains. ”

Liu Bei thought that Li Su was changing the topic, and disdainfully commented: "Is this important?" ”

Li Suwei shrugged: "Sun Tzu said, those who treat those who are not safe win, and it is always right to know more geography for the generals." When I read history, I was always curious about how the Marquis of Huaiyin helped Emperor Gaozu to secretly Chen Cang, and asked the local geography of the Turen, maybe it would be inspiring. ”

Liu Bei chuckled lightly without malice: "Then the virtuous brother pondered slowly, what if you know this kind of thing, you can't go back hundreds of years ago and help Emperor Gaozu fight better." ”

Fortunately, Liu Bei is a real normal person and doesn't know the concept of "crossing", otherwise, he should have said, "You can't travel back to help Gaozu again".

Li Su quickly found an old local medicine farmer who was detained by the army, politely divided a piece of donkey meat from the other party to burn, and asked about the river.

The old peasant replied: "General, this stream can indeed flow all the way to the bottom of Chencang City, and the maximum amount of water is about the end of February, and it can also flow into the moat south of Chencang City, and finally enter Weishui!" I have been collecting medicine here for a long time, and I often go to Chencang to sell goods, so I know it. However, this river is not very common, and the snow melts for a month or two every year, and the rainiest year does not exceed three months, and the rest of the time it is dry. ”

Li Su's heart moved: Could it be that when Han Xin secretly visited Chen Cang, he used water transportation? So the logistics are easy to solve? But why did Zhuge Liang only take the Qishan Road under Wudu County during the Northern Expedition, but he couldn't break through Chencang?

Is Hao Zhao too strong in defending the city, or is Zhuge Liang's logistics too weak to continue to transport grain to the front line of Chencang to maintain the siege of Chencang? If it is too difficult to continue to transport grain to besiege the city, is it because Zhuge Liang did not use water transportation? Or is the season he chose to send troops different from Han Xin, so it is not a wet season?

This series of questions made Li Suru, who had always taken three or five steps one step at a time, feel like a bone in his throat, and he wanted to clear his doubts, so he sincerely asked: "When the river has the largest amount of water, how deep can it be?" Can you go boating? ”

The old medicine farmer shook his head: "The deepest time is only four or five feet, and the strange rocks are messy, how can you walk the boat?" ”

Li Su touched his chin and secretly thought: It seems that it is not a matter of the season, no matter what season the water level of this creek is, it cannot be transported by boat.

That's it, think of this step first, make a good record, and calm Zhang Lu in the future, and come back to slowly investigate the terrain when you have time.

Zhuge Jin, who was always following Li Su on the side, couldn't help but wonder when he saw this: "Why does Zhonglang focus on these useless little things?" You might as well talk about it, maybe your subordinates can help you investigate. ”

Li Su said casually: "I just want to know if the stream in this Chencang Valley has always been so shallow, and in the future, I will have time to ask the soldiers to dig up the gentle slopes on both sides of the river, cut off the soil of the trees, and look at the rock formations on the mountain wall." ”

Li Su studied diplomacy in his last life, and his grades in geography were still very good, although geography was considered a science subject from a scientific point of view, but when the college entrance examination was divided into subjects, he was divided into liberal arts, and there were more things to memorize.

Second, studying diplomacy requires a very deep understanding of various international rivers, and it is necessary to know the situation "since ancient times". Therefore, after two years, Li Su still knows the historical trajectory of the Brahmaputra River, the Ivallody River, the Nu River, and the Lancang River (Mekong River), and where they flow through foreign countries and enter the sea.

This is because diplomats must use all the tricks of "taking advantage of international treaties to build water conservancy projects upstream" to threaten their downstream neighbors within the framework of international law and force them to make concessions and accept diplomatic blackmail.

Relying on the study of this course, Li Su also knows a little about the geographical exploration experience in water conservancy. As long as he dug up the soil next to the riverbed, he could see that the rock type on the mountain wall was sedimentary rock and shale; Or basalt, granite.

If it is the former, it means that the reason why the valley floor is so deep is that it was carved out by water erosion in history, and there used to be a river but now there is no river. If it is the latter, it means that there has been no river here since ancient times, and it is completely due to the accumulation of crustal movements on both sides to form mountain peaks, and this is naturally a trough.

Zhuge Jin didn't know the geographical knowledge, he just silently recorded the situation that Li Su wanted to know, and prepared to go back and look through the classics when the time came, supervise the soldiers to dig the ground and investigate, and help Zhonglang do these small things within his ability.

……

In the East Wolf Valley, the three armies finally crossed the highest point of the Qinling Valley Road in this area in early February, and then began to go downhill, arriving in Hechi County on the fifth day of the first month.

This is a small plain of the river valley with a circle of dozens of miles, you can take a break, and the southern suburbs of the county are more than ten miles away from the Western Han River.

After arriving here, Guan Yu temporarily served as a guide, leading 2,000 troops to open the way, leading the way for Yu Fuluo, heading due west and tracing the upper reaches of the Western Han River along the river valley.

Eighty miles to the west of the river pond is the lower identification, from the lower identification to the west eighty miles is the Wudu, the north of the Wudu is the Qishan Avenue, you can go to Tianshui County to govern Ji County.

Li Su also personally surveyed the surrounding area, and then he had a real understanding: in history, the Ji Han army wanted to go north from Hanzhong, as long as it did not take the Meridian Valley but the northwest direction, then there was no fork in the road from Yangping Pass to Hechi, just one road.

After arriving at the river pool, it will fork, and the road that Guan Yu escorted Yu Fuluo to raise Ma Tuntian in Zhongzhong is the easiest to take, that is, Zhuge Liang often goes out of Qishan. And the other is the way Liu Bei and Li Su came this time.

The movement of Yu Fuluo's army is equivalent to "going south from Chencang into the Qinling Mountains, and then going north to re-detour after reaching Wudu", this posture is also very deceptive strategically, because it can be disguised

"Huangfu Song led the main force of the Han army to pursue Han Sui in the Weishui River Valley of Longshan, but Han Sui slowly retreated because of the blockage of the valley, and the defeat was not chaotic, resulting in Huangfu Song having no space to deploy troops in a roundabout way and outflank Han Sui's back road", so "Liu Bei was invited to make a surprise attack, go to the Qinling Mountains to bypass Longshan, and appear behind Han Sui in Tianshui, and block Han Sui in the Weishui River Valley of Longshan from the back."

This logic is a bit twisted, but if the current general deceives him like this, he can at least understand it.

Because of this, along the way, when Liu Beijun seized the merchant travelers, medicine farmers, and hunters to temporarily detaine, he also told them in a conclusive manner, "Our army took this road to sneak attack Han Sui's back, and the purpose was to go around the Qishan Road to Tianshui."

In this way, if these people have Zhang Lu's meticulous work in public and escape, it will still not make Zhang Lu immediately alert.

Li Su is so yin, even the prisoners who don't plan to let go have to be deceived, and the deceptive scenes must be done in a full set.

This is called acting!

The day after Yu Fuluo was divided into troops to the west to make a feint, on the sixth day of the second lunar month, Li Su also took hundreds of elite scouts, under the cover of Zhao Yun, and prepared to quietly go south to personally survey the terrain outside Yangping Pass.

Liu Bei also wanted to grasp the information of the battle situation, and insisted on personally going to visit Jiancong lightly, and had to bring a few fierce generals to protect him, all of whom were disguised as caravans.

All the way south, Li Su did not travel in vain, but always maintained his vigilance and observation records, how many roads he walked every day, and how far the future army wanted to sneak attack in one day, he made detailed records.

As for the method of measuring the road, he asked the soldiers to actually count the steps, each of which was 5,000 steps, and then changed people to rest their minds, and finally summed them up. In this way, the disadvantage of not being able to see the actual route clearly by looking at the map can also be solved.

This kind of careful and cautious measurement of the distance made Liu Bei and Lu Su and other guards and generals with the army amazed, and secretly praised Li Zhonglang, the pre-war staff officer, for doing too much detail.

"It is about 70 miles in a straight line from Hechi to Wuxing, but along the way to twist and turn along the West Han River Valley, the actual journey is 110 miles, and the mountain road really can't see the straight line distance.

Wuxing to Fu County straight line 30 miles, the mountain road is actually 50 miles, Fu County along the water to Yangping Pass 15 miles, the actual is also 15 miles, this section of the river is very straight. Our army rode half on horseback and half led the horse, and marched lightly for two days. ”

When there were still ten miles left from Yangping Pass, the road exploration work was finally completed, and Li Su and Liu Bei quietly climbed up the hillside to look at Yangping Pass, and checked the mileage of the road.

If you want to attack Yangping Pass suddenly in the future, it seems that it is still too late to start from Hechi, unless you first walk all night and night, rush to Wuxing, take a short rest, and then go from Wuxing to Fuxian at dawn, so that you can walk seventy miles in a day, but it is still within the limit of the mountain road march.

This time, because Zhang Fei was still recovering from his injury, he didn't follow, and there were many fewer reckless people around Li Su who questioned him.

In the end, Dian Wei, who only had one accompanying guard, was a little impatient: "Zhonglang, if you want me to say, what are you doing, just lead the troops to attack Yangping Pass and try it?" ”

Li Su reprimanded: "Nonsense! I waited for a lot of hardship, just for this opportunity to suddenly attack, and asked Zhang Lu not to be alert in advance until the moment of tackling the problem. Yangping Pass is dangerous in the world, once it is exposed, it is possible that it will not be able to attack it for several years! ”

Li Su knows the lessons of history too well, he doesn't need to look at the Romance of the Three Kingdoms, as long as he looks at the romance, he knows that in history, the northern regime concentrated all its efforts to attack Yangping Pass, but all the battles of bright cars and horses have never been broken.

The only two records were Cao Cao's conquest of Zhang Lu and later Zhong Deng's annihilation of Shu Han.

When Cao Cao conquered Zhang Lu, he relied on piling up troops at the beginning, and it was useless for hundreds of thousands of troops to fight for so long. In the end, it was Zhang Lu's younger brother Zhang Wei's brain pumping, and he took the initiative to go out of the customs to fight back, but was chased and killed by Xiahou Yuan in ecstasy.

When Zhong Hui entered Hanzhong, he relied on the surrender of traitors, and the second was that Jiang Weitun Tianzhong was blocked by Deng Ai on the way back to Hanzhong, so the morale of the Yangping Pass defenders was extremely low.

In other words, the two breaches in history were only broken by "deceiving the enemy's main force defending the pass, or isolating them from the outside and not returning to the pass for defense" without using epoch-making scientific and technological siege weapons.

As for the routine of "imitating Deng Aizhong to attack from Longyou and Guanzhong", now I can't even think about it, it doesn't conform to the actual situation at all. The premise of that move is that Jiang Wei is already outside the gate and can be isolated and contained by you. Now Zhang Weigou has to be like a turtle, the whole army is shrinking, what to divide it.

If Li Su wants to make a strategy, his thinking inertia must also be "how to deceive and destroy the main force of the enemy's garrison troops", and then tackle key problems.

"Yangping Pass is so majestic and treacherous, the reason why I have always secretly marched into the army is to see if there is a way to catch an opportunity for a sneak attack when the main force of the enemy army is negligent. Either the main force guarding the pass changed its defense and returned to Hanzhong, or the main force guarding the pass was suddenly deceived out of the pass by our army under the pretext of being confused, and then suddenly killed. If it weren't for that, this battle wouldn't be easy. ”

Li Su observed the terrain again and again, and consulted with Liu Bei and Lu Su.

The situation when Zhang Wei made a fool and took the initiative to attack when he met Xiahou Yuan was a once-in-a-century situation.

Li Su can't pin his hopes on the enemy's once-in-a-century shark arm again, he can only take the initiative to promote it.

"Even if there is no imperial army nearby, no matter how good the secrecy is, Zhang Wei will not be stupid enough to get out of the customs, right?" After listening to this, Lu Su on the side thought about it again and again, and really couldn't think of how the enemy could be so mentally retarded.

"Can you count on Zhang Lu to force Zhang Wei out of the customs to fight after the battle begins?" After Li Su was poured cold water by Lu Su, he inevitably retreated in his heart, expecting Zhang Lu to misjudge the situation like Li Longji, and force Zhang Wei to go out of Yangpingguan in the decisive battle like Li Longji forced his brother Shuhan out of Tongguan.

But soon this unrealistic fantasy was also driven out of his mind by himself: Li Longji's mental retardation during the battle of Tongguan was no longer a once-in-a-century but a once-in-a-millennium encounter, and that was even more unexpected.

Along the way, Liu Bei and Li Su and their entourage gradually touched closer to Yangping Pass and approached to observe the details.

At this moment, Li Su suddenly found a question: "Huh? I was careless! The road in front of Yangping Pass, why didn't it go straight into the pass and stand up? Rather, it is a herringbone road, and Yangpingguan is built at the top of the intersection of this herringbone?

Doesn't that mean that if you don't want to enter Yangping Pass and go to Hanzhong, but you just want to enter Shu and go to Chengdu, you can 'pass through Yangping and pass by without entering'? ”

Li Su thought down this line of thought, and his heart was shocked.