Hangu Pass was the eastern gate of the Qin State during the Warring States period, and was an important pass for the Qin State to resist the attack of the Six Kingdoms of Shandong, and in the Qin and Han Dynasties, with the unification of the world, the strategic position of Hangu Pass had actually begun to decline. Although Emperor Wu of the Han Dynasty built a new Hangu Pass, it was not built on the site of the Qin Pass Pass, but moved 150 kilometers to the east. At the end of the Eastern Han Dynasty, in order to prevent military rebellion in Kansai, Cao Cao built Tongguan and abandoned Hangu Pass, which has since withdrawn from the stage of history.
Qin hangu pass: the throat of Guanzhong and Kanto, an important pass for the Qin state to resist the six kingdoms of Shandong
The so-called Hangu is actually just a crack in the thick mulberry plain. Chou Sangyuan is a typical loess plateau topography, although the top is flat as plain, but the height is very high, the surrounding cliffs are steep, the Yellow River flows from the north of Chou Sangyuan, close to the original wall, so that guanzhong and Kanto want to go back and forth, there is no other way to go, only through this crack.
Although this road is called Hangu Road, it is actually not more than a few meters wide, but it is a real "car cannot square tracks, horses cannot saddle together", which can really be described as "mud pills can be plugged", and Hangu Pass is located at the opening of this crack, that is, today's Wangduo Village in Lingbao City, Henan Province.
Hangu Pass
To the east of Hangu Pass, in front of Hangu Pass, is the Hongnong River, which in ancient times was not as small as it is today, and this river formed the natural moat of Hangu Pass. If the enemy wanted to attack Hangu Pass, he had to cross the Hongnong River first, and since the Hongnong River flowed close to the east side of the Chou Sang Yuan, there was only a narrow narrow road between the river bank and Guancheng Castle, and the army could not be lined up at all.
So is it possible for ancient marching armies to fight wars to bypass Hangu Pass? It's not actually possible. The reason is that the ancient thick mulberry plains are densely forested (from the name of the thick mulberry plains is not difficult to see the density of the forest), from the Kunshan Totongjin road of more than a hundred miles, there are dense forests everywhere, and in ancient times, it was also known as "the plug of the peach forest" and "the plug of the pine cypress". Because the forest is so dense, it is difficult for pedestrians to pass, let alone the army. Therefore, as long as this crack is held, it is equivalent to cutting off the east-west traffic.
It is precisely because of this natural geographical advantage that the six kingdoms of Shandong have repeatedly attacked the Qin state, but they can often only look at Guan Xingsi. For example, in the third year of King Shenliang of Zhou (318 BC), King Huai of Chu raised the division of the Six Kingdoms to cut down Qin, and Qin Yihangu was in danger, causing the army of the Six Kingdoms to "ambush millions of corpses and bleed and drift". Another example is that in the sixth year of the reign of the Qin Dynasty (241 BC), the armies of the five kingdoms of Chu, Zhao, and Wei invaded Qin, and "to the Hangu Valley, they were all defeated."
Qin Shi Huang
It is precisely because of the Hangu Pass that from the Spring and Autumn Period onwards, this place has become a place of contention for soldiers, and the State of Jin once sent troops to garrison this place to curb the eastward advance of the State of Qin, and after the decline of the State of Jin, this place was taken by the State of Qin, and eventually became the frontier position of the State of Qin that could be attacked and retreated.
Hanhan Valley Pass: Emperor Wu of the Han Dynasty moved the Hangu Pass 300 miles east, which has actually lost its role
As to why Emperor Wu of han wanted to move Hangu Guandong, there is still no accurate explanation. According to tradition, although the general Yang Shu of Louchuan was given the title of Marquis for his merits, he was given the title of Marquis of Guanwai because he no longer had a fief in Guannei. In order to avoid the ridicule of others, Yang Shu wrote to Emperor Wu of Han, asking that the Kanto of Hangu be moved to the territory of Present-day Xin'an, which could not only expand the territory of Guanzhong, but also strengthen the control of Kwantung, and finally obtained the consent of Emperor Wu of Han, and in this way, his fiefdom was also included within Hangu Pass, and he became the Marquis of Guannei.
In any case, the reason why Emperor Wudi of the Han Dynasty agreed to relocate Hangu Pass was mainly due to the decline of the strategic position of Hangu Pass. Since the Qin and Han dynasties, the world has been unified, and there is no need for confrontation between Guanzhong and Guandong, so the strategic position of HanguGuan will inevitably decline. Although there were a large number of clan kings in Shandong at that time, after the "Rebellion of the Seven Kingdoms", the strength of the clan king had been greatly damaged, and after Emperor Wu of the Han Dynasty implemented the Tuien Order, the area under the jurisdiction of the central imperial court was bound to go out of Guanzhong, go deep into all parts of Shandong, move east to Hangu Pass, and strengthen control over Kwantung, which was indeed in line with the imperial court strategy.
Liu Che
In addition, due to the continuous cutting of the Yellow River channel, the water level of the Yellow River was constantly decreasing, and the river channel that was originally attached to the thick mulberry plain was exposed to form a river beach, and the Kwantung army could completely take the river beach to bypass the thick mulberry plain, without having to take the Hangu Road. In addition, the trees on the thick mulberry plains have long lost their natural barrier effect due to excessive logging, and the Kwantung army can also go to the thick mulberry plains. All this has made the strategic role of Qinhan Guguan decline.
However, after moving east, Hangu Pass also lost its role in guarding the gate of the Middle East. It is not difficult to see from the map that from Luoyang to Guanzhong, there are actually two roads to go, the North Ridge Road and the South Ridge Road, while the Hanhan Valley Pass is located on the North Ridge Road. In this way, if the rebels wanted to enter Guanzhong, they could completely take the South Ridge Road, thus bypassing the Hanhan Valley Pass. For example, in the last year of Xinmang, when the Chimei army invaded Guanzhong, the soldiers directly bypassed the Hanhan Valley Pass in two ways and would be in Hongnong County (that is, Qinhan Valley Pass), and at this time, the Qinhan Valley Pass had been abandoned, and as a result, the Chimei Army easily attacked Guanzhong.
Tongguan: After the Three Kingdoms, the strategic role of HanguGuan disappeared, and Tongguan began to become a strategic location
After the Battle of Chibi, Cao Cao saw no hope of going south, so he began to shift the strategic focus to Xiliang, in order to prevent the Guanxi military rebellion, coupled with the reduction of the strategic role of QinhanGuguan, Cao Cao began to set up Tongguan in the first year of Jian'an (196), and Qinhanguguan completely withdrew from the historical stage. As for Cao Cao's order xu chu to build a grain transport road on the Yellow River beach, and Hongnong Taishou Meng Kang to build the "Wei Han Valley Pass" on the grain transport road is a later story.
Cao Cao
Tongguan is located at the confluence of the Wei River and the Yellow River, opposite the important ferry of the Yellow River, Fengling Ferry, which is also an extremely dangerous place. In the south of the Yellow River, there are two rivers, namely Tongshui in the west and Yuanwanggou in the east, and in the middle of the two rivers there is a mountain, two kilometers wide and seven hundred meters high, because both sides are washed by water all year round, so the cliffs are steep and very steep.
To the north of the yellow river is the Yellow River, and like Hangu Pass, the Yellow River flows close to the body of the body, without any gaps, so that everyone who travels west must pass through the plain, and there is no other way to go. To climb the hill, there is only one road that can be passed, called Huang xiangsaka. Like Hangu Road, Huangxiangsaka is only a few meters wide, and it is also a dangerous place where everyone can't open it. And along the Yellow Lane, you will reach Tongguan.
However, Tongguan encountered the same problem as Hangu pass, that is, the change of terrain. When Tongguan was first built, the Yellow River north of Tongguan was also flowing close to the body, and if you want to pass through Tongguan, you can only climb the plateau to pass. However, as the Yellow River continued to wash away the river, the yellow riverbed north of Tongguan continued to decline. By the time of the Tang Dynasty, Tongguan also appeared a bare Yellow River beach, resulting in the natural danger of Tongguan no longer existing, and the Tang Dynasty had to move Tongguan out of the mound and move to the river beach.
Tongguan
When the Tang Dynasty moved Tongguan from the mountain to the river beach, the old Tongguan was abandoned. Instead, the twelve passes, known as the Twelve Cities of the Twelve Cities, were garrisoned by officers and soldiers in peacetime, and ordinary people were forbidden to pass through. However, in the late Tang Dynasty, the system was corrupt, and it was not fortified at the Twelve Cities, resulting in the rebel army of Huangchao directly circling from the old Tongguan to the back of the Tongguan on the river beach, and attacking the Tongguan from front to back.
In general, Hangu Pass and Tong Guan are inheritance relations. During the Spring and Autumn Period and the Warring States Period, the State of Qin attacked the Six Kingdoms of Kwantung based on Guanzhong, so the strategic position of Hangu Pass was extremely important, and there was no Tong Pass at that time. During the reign of Emperor Wu of the Western Han Dynasty, the old Hangu Pass was replaced by the new Hangu Pass, but the effect was not obvious, and then the construction of Tong Pass began, and as a result, the Tong Pass lost its role due to the change of terrain.
Of course, whether the pass is dangerous is only on the one hand, on the other hand, it depends on the strength of the country, if a country is decayed, then even if the pass is no matter how dangerous it is, it is difficult to keep.