On the west bank of the Yalu River, the Tang army led by Li Shimin slowly arrived here, and then set up camp on the bank, and on the opposite side of the river, there was a tall and steep pass, which was the last line of defense in Pyongyang City.

Li Shimin has a habit of fighting, that is, he likes to check the terrain in person, so as soon as the army arrived here, he took Li Xiu, Cheng Yanjin, Li Ji and others out of the camp together, and came to the Yalu River to look at the Bogou mouth on the opposite side.

Bogou is actually a valley formed by the fracture of a mountain range, originally this is the southernmost branch of the Changbai Mountains, an endless mountain range and the Yalu River parallel, but to the location of Bogoukou, it suddenly seems to be broken, turned into a valley, on both sides are steep mountains, almost impassable, and the valley is the only passage, so the Goguryeo people imitated the topography of the valley, built a pass in the valley, that is, Bogoukou.

"What do you think?" Li Shimin looked at the other side for a long time, and then suddenly asked the ministers behind him.

"Your Majesty, this Bogou Pass is not easy to fight, not to mention that this pass is built so steeply, just the Yalu River in front of it is not good, because the pass is too close to the river bank, it is equivalent to a natural moat, if we want to attack the pass, we must cross the river, but the other party can give us a fatal blow when we cross the river!" I saw Cheng Biting Jin being the first to frown at this time and said.

"What General Cheng said is that the other party's pass is too close to the river, and there is no place for our army to camp, so a frontal attack will definitely not work, the best way is to find a place with a slower flow to cross the river in the upper and lower reaches of the river, but the mountains on both sides of the Bogou mouth are close to the river, and there is no way to go on both sides, which is troublesome." At this moment, I saw Li Daozong also speak.

Bogoukou is a valley, from the front of Li Shimin and they stand, the mountains on both sides of the Bogou valley are in the shape of "eight", just extending to the riverside, and there is no way to go on both sides, only to cross the river from the front.

Li Xiu was also observing the topography of Bogoukou at this time, in fact, in his opinion, Bogoukou was more like a river valley, where there should have been a river rushing through the mountain range and then converging to the Yalu River, but later the river dried up, so a triangular alluvial plain was formed, and the mountains on both sides extended to the river, the apex of the triangle was Bogoukou, and the triangular plain in front was too small, which was very unfavorable for the army to develop a formation.

"A frontal attack is not completely impossible, for example, as long as we can set up a pontoon bridge on the river, and then send troops to defend the bridge, we can send a steady stream of troops to the opposite bank, but the terrain on the opposite side is narrow, and the troops sent over each time are limited, so if you want to take down this ditch mouth, I am afraid you will have to pay a lot of price!" At this moment, Li Ji, who had not spoken, finally spoke.

"The Goguryeo people on the other side will never let us build the pontoon bridge easily, and even if they do, they will definitely send troops to destroy it, just if we want to defend the pontoon bridge, we have to pay a lot of casualties, plus the casualties of this pass, this price really makes me feel distressed!" Li Shimin also frowned at this time and said, an experienced general like him can generally estimate the approximate price he needs to pay before the war.

"How many troops do you have in Bogoukou now?" After a while, Li Shimin suddenly asked again.

"Originally, there were 30,000 troops stationed here, but 20,000 were later taken away by Gao Yanshou, but according to the information that came some time ago, Quangai Suwen seems to be intending to send more troops to Bogoukou, and I don't know how many people are in the city now?" Cheng Yanjin immediately replied at this time, the terrain of Bogoukou is dangerous, as long as the city gate is closed, the news east of the Yalu River will hardly be transmitted, so they don't know if Quangai Suwen has sent reinforcements?

"The army rests for two days, and after three days, test the reaction of the other side, and then you should know how many defenders there are in your mouth!" Li Shimin immediately ordered, since he didn't know the reality of the city, he could only use human life to test, although it was cruel, but there was no good way.

"Your Majesty, calculate the time, Su Dingfang's army should also land, maybe it will attack Pyongyang soon, and then maybe you can attack Bogoukou from behind, if you can attack it from front and back, Bogoukou may not be so difficult to fight!" At this moment, I saw Li Xiu suddenly walk forward and speak.

Li Xiu felt that Su Dingfang's cavalry could definitely play a key role, but Li Shimin shook his head when he heard his words and said: "Su Dingfang only has more than 10,000 people, and most of them are cavalry, and the order I gave him is to harass Pyongyang as much as possible, and at most it will interrupt Pyongyang's transportation of supplies to Bogoukou, and I don't expect them to take Pyongyang City, and we need to find a way to solve the Bogoukou in front of us." ”

Hearing Li Shimin say this, Li Xiu then remembered that Su Dingfang's subordinates were indeed all cavalry, and this kind of thing attacking the city was indeed not what they were good at, of course, if a Tang cavalry suddenly appeared around Pyongyang City, and Pyongyang was still the richest place in Goguryeo, then they could completely repeat what Su Dingfang did on the border of Goguryeo, and even cut off Pyongyang's contact with the outside world, which was Su Dingfang's strategic goal.

At that moment, Li Shimin and the others stopped by the Yalu River for a while, and then returned to the camp to rest, but they didn't notice that when they left, there was a person at the head of Bogoukou City who was looking at them with a telescope, and this person was Quangai Suwen, who had just arrived at Bogoukou.

Quangai Suwen left Pyongyang a few days ago, and finally arrived at Bogoukou the day before yesterday, and the result was really a coincidence, only two days later, the Tang army also arrived at the Yalu River, so he also immediately climbed to the top of the city to look at the Tang army on the other side of the river, but he didn't expect to meet a group of people who came to the riverside, although he didn't know Li Shimin, but from the behavior of these people, he could also guess the identity of these people, especially when he saw Li Shimin, who was the leader, his eyes burst out with a fine light.

"Father, is that person the emperor of the Tang Dynasty?" After Li Shimin and his party left, Quan Nanjian, who was standing next to Quan Gai Suwen, suddenly asked, he also saw that the group of people on the opposite side had an extraordinary background, especially the person who was the leader, and he was like a star holding the moon by the people around him, and he knew that his status was extremely high at a glance.

"Judging from the respect of the people around him, he should be the legendary Emperor of the Tang Dynasty." Quan Gai Suwen nodded immediately, and at the same time, there was a complicated look in his eyes.

From a standpoint, Li Shimin is the enemy of Quangai Suwen, but in terms of personal feelings, he admires Li Shimin very much, after all, the age difference between the two is not much, but the other party leads a huge empire, and when he was young, he was even more successful, in contrast, he could only stay in small Goguryeo, and he could not be compared with Li Shimin at all.

"Folklore has it that the Emperor of the Tang Dynasty is too tall and can tear tigers and leopards alive, but now it seems that this is no more than that, and he even looks a little old, not like the emperor of a big empire at all." Quan Nanjian said with some disdain at this time, although he was a little far away, and the telescope was not very clear, but Li Shimin's gray beard was very conspicuous, and his movements were also a little old, which was very different from what Quan Nanjian imagined.

"How can you believe the words of the fools of the people? And as an emperor, the most important thing is wisdom, not to mention that the Tang Dynasty is like a cloud, where is the use of him to go into battle in person, as long as he gives an order, there are countless soldiers who will die for him, this is the terrible thing about the Tang Emperor! When Quan Gai Suwen heard his son's words, he couldn't help but reprimand with a straight face.

The reason why Quan Gai Suwen left his eldest son, Quan Nanjian, instead of Quan Nanjian, is mainly because Quan Nanjian's character is impulsive, and his personality is also a little arrogant, not as calm as Quan Nanjian, if he is allowed to stay in Pyongyang, if he is defeated here at Bogoukou, I am afraid that he will only fight desperately with the Tang Army, instead of honestly retreating to Marudu City.

"Father, the Tang army is already here, do we have to be prepared, as long as the Tang army starts to cross the river, we will kill it and teach the Tang army a hard lesson!" Quan Nanjian said again at this time, after coming to Bogoukou, he was more confident in the terrain here, and even felt that this place was simply a one-man pass, and he could rely on the terrain here to block the footsteps of the Tang army, as long as it dragged on until winter, the Tang army could only retreat.

"Preparation must be prepared, but the most important thing now is that the whole city is under martial law, and no one is allowed to go out of the city, after all, there are many people who are looking forward to the arrival of the Tang army, and secretly report to the Tang army, I estimate that the Tang army still doesn't know that we have arrived at Bogoukou, and when they attack the city, let's give them a 'surprise'!" When Quan Gai Suwen said the end, a bit of murderous intent flashed on his face.

Time passed quickly, early in the morning of the third day, the Tang army finally began to cross the river, although the Yalu River is not as wide as the Yangtze River and the Yellow River, but it is also about a mile, even the narrowest place, there are four or five hundred steps, even the bow and arrow can not shoot through, so it is not easy to cross the river.

However, as the so-called people are easy to do, the Tang army camp with a lot of craftsmen, in fact, it is equivalent to the engineering soldiers of later generations, they soon began to cut wood on the spot, and then build a pontoon bridge, at the beginning it was very smooth, but in front of the pontoon bridge is about to reach the opposite bank, Bogou mouth suddenly rushed out of a Goguryeo army, rushed to the riverside after a burst of rockets, in the blink of an eye on the pontoon bridge everywhere, the pontoon bridge burned down after working hard for most of the day, and some craftsmen were killed and injured.

Seeing this situation, Li Shimin was also angry, but there was no good way, so he could only order the craftsmen to build it again, and this time several pontoon bridges were built together, but it had no effect, countless times, and in the end it was impossible to escape the fate of being burned, and even the pontoon bridge could not be built, let alone the river, and the Tang army was also in a predicament all of a sudden.