Li Chao stood in Loufan Pass City and patrolled the Pass City with Su Dingfang and others.

Next to it is Princess Pingyang who arrived one step ahead of Li Chao. She has taken over as the governor of Lanzhou. Loufanguan is a prominent part of the northeast of Lanzhou, sandwiched between Shuozhou and Daizhou.

"Master, Loufan Pass is located on Huagai Mountain in the remaining veins of Hengshan Mountain. It is located on Huihe, overlooking the east, west and south sides, with four miles in length, and there are three gates in the east, west and south. After the two generals Li Ji and Li Jing guarding the river from time to time, the city is now five miles around the city, with a base of five meters, two and a half meters wide, and a city is more than three meters high. There is also an outer Guancheng, which is built by rammed earth, with a circumference of seven miles, and a north gate. There is a flying tower on it, named Zhenshuolou. Because the building is as high as a phoenix spreading its wings, it is also called Phoenix City."

Standing on the high city wall of Loufan Pass, looking out to the north, you can see far.

This pass city is narrower in the north and south and long in the east and west. It now has two pass cities, inside and outside, with a circumference of more than seven miles. The city walls are tall and strong, with arrow towers around and enemy towers scattered.

The inner city wall increased from more than three feet to four feet.

Several city gates were covered with bricks, and a towering moat fort was built on the top of Huagai Mountain in the north of the city. There are three-story heavy buildings on the pier, called Huagai Tower.

This Loufan Pass is not only connected to the inner Great Wall, but also built a forty-mile side wall in the north of the city.

The reason why Li Chao knows these things very well is that the entire Lou Fanguan reinforcement plan was originally written by him.

The Tang Dynasty did not build the Great Wall, but the Turks in the north were powerful. Therefore, when Li Shimin ascended the throne, Li Chao advanced a northern defense plan to Li Shimin. He suggested that Li Ji and Li Jing, two generals, guard Hebei, and at the same time, focus on building several passes in Hedong, Hebei to defend Turkic fortresses.

Li Chao's fortress plan is centered on the three internal and external barriers of the Ming Dynasty.

After reading the plan and discussing it carefully with Li Chao, Li Shimin finally adopted this suggestion and did not repair the Great Wall, but focused on strengthening the three internal and external barriers.

The focus of the Tang Dynasty's defense in the north was no longer the line, but six points.

Loufan Pass was Ningwu Pass, one of the three outer passes during the Ming Dynasty.

Ningwu Pass was called Loufan Pass at this time, so this place was from the Loufan tribe in ancient times. During the Warring States Period, King Wuling of Zhao established Loufan Pass here to prevent the Huns. During the Northern Wei Dynasty, Guangding and Shenwu counties successively governed this place, and in the Sui Dynasty, they belonged to Gan County and Jingle County. At this time, the imperial court established Lanzhou, and Loufan Pass belonged to Jingle County, which intersected with the two states of Shuo and Dai.

Later, the Tang Dynasty established Ningwu County, which was the beginning of Ningwu Pass. It was named Guangning and Shenwu County two characters, but at this time, it was still called Loufan Pass.

However, although this place is called Loufan Pass, its defense, after the reinforcement of the two generals Li Ji and Li Jing in the past two years, the danger of this pass is no less than that of Yanmen.

The three inner and outer gates of the Great Wall that Li Chao originally proposed were Pianguantou and Yanmen Pass and Loufan Pass, and the three inner gates were Juyong Pass, Zijing Pass, and Daoma Pass.

The outer three passes are located in the northwest of the northeast of the river, and are connected to the inner Great Wall line between Bitou, Ningwu and Yanmen Pass. It is a huge barrier that stretches 500 miles north of Shanxi, and uses the dangerous terrain of the Great Wall and Hengshan in the past.

Unlike the concept of operating the Great Wall in previous dynasties, Li Chao proposed the defense plan for the three inner and outer gates of the north, although it was based on the Great Wall, but not linear defense, but a defense cluster with several important nodes as the core, supporting each other from all directions, is a point-shaped defense network.

The Turks dominated the north, especially in the situation where Daibei and Hetao occupied, Hedong and Hebei were the most easily attacked and broken through. Once they broke through the line of the Great Wall, they could enter the plain area, especially the Hebei Plain. If the Turks were allowed to enter the Hebei Plain, it would be extremely difficult to defend against Turkic cavalry in the vast plain area.

For this reason, Li Chao proposed the defense plan for the three inner and outer barriers in the north.

He abandoned the two defensive layers of the Great Wall in the past, but instead formed two lines of the outer and inner sides in the east and west directions in the north, changing the north and south defense layers into the east and west defense layers.

In the north of the Taihang Mountains in Hebei, three passes of Bauhinia, Ma and Juyong are set up along the line, and these three passes are used to establish a fortress cluster to form a deep defense circle to protect the Hebei Plain. In the east and west of the Hebei, three passes of Bitou, Loufan and Yanmen are set up, which are the outer three levels, and these three passes are the first level of defense cluster.

Li Chao's defense focus of the three internal and external passes is actually in Hebei. The three internal and external passes are closely guarded to ensure that the Turks cannot go from Hetao and Daibei to the advance bases of these Turks who broke into the Hebei Plain through Daibei.

Under this kind of thinking, they would rather let them break into the central Hedong area than let them enter the Hebei Plain.

The defense tasks of the outer three passes are extremely heavy. The Bithead Pass is on the extreme edge, and Yanmen is the key to rushing, while Loufan Pass is between the two passes, controlling the head of the border pass, and the situation is extremely heavy.

The Turks always thought that the focus of the Hedong defense of the Tang Dynasty was Yanmen Pass. In fact, they didn't know that the northern defense thinking of the Tang Dynasty had long changed.

The imperial court stationed heavily in Loufan Pass, so as to facilitate the protection of Yanmen in the east, the support of Baian Pass in the west, and the departure of Yunshuo to the north.

Li Chao pointed to the continuous valley and said to Pingyang, Su Lie and the others, "The geographical location of Loufan Pass is very special, especially in the current situation occupied by the Turks, if they want to go south, they must pass the three passes. There is a desert Gobi in Shuofang, and it is inconvenient to attack there. Therefore, it is mainly necessary to go south east and go south from here, they must pass the three passes."

"In the three gates, there is the Yellow River as a natural danger in Pianguan, so the Turks who came from Hetao can only step through ice in winter. However, Yanmen Pass has a natural danger and it is difficult for cavalry to break through. Only Loufan Pass, although it is Huihe, the Huihe River is a seasonal river, and there is a period of time to cut off every year. Therefore, in the autumn season, the Turkic cavalry can advance south along the Heguhun Division and go straight to the gate."

The Huihe River Valley is relatively wide, and Li Jing's report to the court said that ten cavalry could advance together.

Because of this unique reason, the middle road Loufan Pass, which is the three outer gates, has become a node that is easier to break through. However, the Turks do not know that many fortress clusters have been built here, and Loufan Pass has become a war fortress of the two-story gate city around seven miles and inside and outside.

The dot-shaped fortress defense cluster has one advantage over the previous Great Wall linear defense, which is that it can support combat independently and is not easy to break through.

Compared with the linear defense of the Great Wall, this method of defense is far inferior to that of the Great Wall for small rafts of grassland cavalry. Because the Great Wall is a comprehensive defense, small rafts of cavalry cannot break the city wall or pass through the pass. Only when a large number of grassland cavalry goes south, the Great Wall will appear weak, and Gaokou, Great Wall and passes are difficult to cope with a large number of cavalry.

The point-shaped fortress cluster created by Li Chao is different. The focus is on the fortress and surrounding piers, etc., which are point-shaped. There will be gaps in the middle of the castle. Small groups of cavalry can easily penetrate in. If they just come to rob, they cannot completely defend themselves. However, if they are defending against large groups of cavalry, these fortress groups can support each other and support defense, which is difficult to break for the time being.
Chapter completed!