During the Warring States Period, the key pass Hangu Pass gradually lost its strategic significance, and it was finally abandoned
Hangu Pass was an important pass for the Qin State to resist the attacks of the Six Kingdoms of Shandong during the Warring States Period, but with the unification of the whole world during the Qin and Han dynasties, the strategic position of Hangu Pass actually began to deteriorate. Although Emperor Wu of the Han Dynasty built the Hangu Pass, he did not intend to replace the old Qin Pass, but moved the Hangu Pass 150 kilometers east. At the end of the Eastern Han Dynasty, Cao Cao built Tongguan in order to prevent rebellion in the Western Regions, and abandoned Hangu Pass, which disappeared in history.
Qin Hanging Pass: The key pass between Guanzhong and Guandong is an important pass for Qin to defend the six kingdoms of Shandong.
The so-called Han Palace is actually just a crack in the birdsong ping. Niaomingping is a typical woodland plateau terrain, its top is as flat as the original Niaomingping, but the height is very high, surrounded by steep cliffs, the Yellow River flowing from the north of Niaomingping clings to the original city wall, so to go back and forth between Guanzhong and Kanto, there is no other way but to pass through this crack.
Although this road is known as the Hangu Road, it is actually only a few meters wide, and it is"A cart cannot be put on the rails, and a horse cannot be saddled"It's really true"Mud pellets can be filled", and Hankou is located at the opening of this crack, which is today's Wangyi Village, Lingbao Town, Lingbao City, Henan Province.
In the east of Hangu Pass, that is, in front of Hangu Pass, there is the Hongnong River, which was not as small as it is now, and it is the natural moat of Hangu Pass. If the enemy wants to attack Hangu Pass, it must first cross the Hongnong River. Since the Hongnong River is close to the east side of the Bird's Nest Plain, there is only a narrow road between the river bank and the pass, so the enemy forces cannot deploy their forces.
But in the past, was it possible for expeditions to bypass Hangu Pass? In fact, it's impossible. The Guping Bird's Nest is densely forested (the name Pingbird's Nest makes it easy to see the denseness of the forest), and the road from the Central Plains to Tongjin is more than 100 kilometers long, and there are dense forests everywhere, which is called in ancient times"Peach grove by the sea"、"Seaside pines! "。This road was also called in ancient times"Peach grove by the sea"with"Seaside pines! "。The forest is dense and difficult for pedestrians, let alone the military. Therefore, as long as this rift valley is preserved, it is equivalent to cutting off east-west communications.
Taking advantage of this natural geographical advantage, the six countries of Shandong have repeatedly joined forces to attack Qin, but they can often only sigh with admiration. For example, in the third year of King Zhou Shenliang, King Chu Huai went to the Qin and Han Tianwei Palace, eliminated the six divisions of Qin, and made the six ** teams"Millions of corpses, bleeding skulls"。For another example, in the sixth year of Qin Shi Huang, Chu, Zhao, Wei and other five ** teams committed Qin"All were defeated and left in the Han Valley"。
The impregnable Hangu Pass in the Spring and Autumn Period became a battlefield for the Jin State to send troops to block the Qin State's eastward advance, and after the fall of the Hangu Pass, the Jin State captured the Qin State, and the Qin State finally lost ground and retreated to the front line.
Hanhan Valley Pass: Emperor Wu of the Han Dynasty moved the Hanhan Valley Pass 300 miles eastward, making it useless.
The reason why Emperor Wu of the Han Dynasty moved east to Hangu Pass is still unknown. The traditional saying is that General Yang Bu was meritorious and was named the Marquis of Guanwai, and there was no fief in Guanzhong. Unwilling to be ridiculed, Yang Dou wrote to Emperor Wu of the Han Dynasty, requesting that Hangu Guandong be moved to Xin'an territory in order to expand the territory of Guanzhong and strengthen his control over Guandong, and Emperor Wu of Han finally approved this request, so his fief was included in Hangu Pass and became the Marquis of Guanwai.
In any case, the main reason why Emperor Wu of Han agreed to relocate Hangu Pass was that his strategic position had deteriorated. Since the Qin and Han dynasties, the world has become more and more unified, and there is no need for Guanzhong and Guandong to exist, so the strategic position of Hangu Pass has to be reduced. Although there are many princes in Shandong, but"Rebellion of the Seven Kingdoms"Later, the power of the princes was greatly reduced. After the implementation of Emperor Wu's proton order, the jurisdiction of the Guanzhong court had to penetrate deep into the Shandong region and move east to Hangu Pass in order to strengthen its control over the Guandong region, which was actually in line with the imperial court's strategy.
In addition, as the flow of the Yellow River continued to decrease and the water level dropped, the river channel that was originally close to the Bird's Nest was exposed, forming an embankment that the Kwantung Army could use to bypass the Bird's Nest without having to take the Hangu Road. In addition, the trees on the Bird's Nest Plain were massively cut down, and the natural barrier was lost, so the Kwantung Army could also pass through the Bird's Nest Plain. As a result, the strategic role of Qinkeng Pass has been greatly reduced.
However, after moving eastward, the Han Pass lost its role as a guard of the gates to the Middle East. As you can see from the map, there are actually two roads leading from Luoyang to Guanzhong, namely Bendao North Road and Bendao South Road, and Hanguan is on Bendao North Road. Therefore, if the rebels want to enter Guanzhong, they can bypass Hanguan and take the southern road of Bendao. For example, in the last years of Xinmang, the Red Mei army bypassed the Hanhan Valley Pass to attack Guanzhong, and joined forces in the then uninhabited Hongnong area (i.e., Qinhan Valley Pass), which made it easy for the Red Mei Army to enter Guanzhong.
After the Three Kingdoms, the strategic position of Hangu Pass disappeared, and Tongguan became a strategic location.
After the Battle of Chibi, Cao Cao, who had no hope of going south, began to shift his strategic focus to Xiliang in order to avoid the rebellion of the Western Liang army. With the decline of the strategic role of Qin Hanguan, Cao Cao began to build a real road in Tongguan in the first year of Jian'an (196), and Qin Hanguan completely withdrew from the stage of history. Cao Cao ordered Xu Chu to build a grain road along both sides of the Yellow River, and instructed Hongnong County Taishou Meng Kang to build along the grain road"Weihan Valley Pass", which is what was planned later"Weihan Valley Pass"。
Tongguan is located at the confluence of the Wei River and the Yellow River, and is far away from Fenglingdu, an important ferry port of the Yellow River, and is an extremely dangerous place. There are two rivers south of the Yellow River, Tongshui to the west and Yuanwanggou to the east. Between the two rivers is a mountainous plateau, two kilometers wide and 700 meters high, which is very dangerous on both sides due to the constant flow of water.
The Yellow River flows north of Ao Bao and, like Hangu Pass, clings to Ao Bao without leaving a gap, so anyone traveling west must cross the plain as there is no other way to go. There is only one road leading to the plateau, which is called Huangxiangzaka. Huangxiangban Road, like Hangu Road, is only a few meters wide, which is very dangerous, and it is impossible for a person to cross at all. After climbing the Huangxiangzaka Highway leading to the plateau, we arrived at Tongguan.
However, Tongguan faced the same problem as Hangu Pass, namely the change of terrain. When Tongguan was first built, the Yellow River north of Tongguan was also close to the Loess Plateau, and if you want to cross Tongguan, you must cross the Loess Plateau to pass the pass. However, with the continuous transport of water from the Yellow River, the course of the Yellow River north of Tongguan has been declining. By the Tang Dynasty, Tongguan also had an exposed part of the Yellow River's bank, and the sacred threat of Tongguan no longer existed, and the Tang Dynasty was forced to move Tongguan from the plateau to the riverbank.
When the Tang Dynasty moved Tongguan from the plateau to the riverbank, it destroyed the old Tongguan. Instead, there were twelve passes, known as the Twelve Liancheng, which were usually managed by officers and soldiers, and ordinary people were not allowed to enter. However, by the end of the Tang Dynasty, the system had become so corrupt that all the passes in the town of Twelve Societies were unfortified, resulting in the Huangchao rebels being able to cross the Tongguan directly from the wooden terraces of the old Tongguan to the riverbank outside the pass, and then break through the Tongguan from the front and back.
In general, Hangu Pass has a hereditary connection with Tongguan. During the Spring and Autumn Period and the Warring States Period, the Qin State used Guanzhong as a base for attacking the six countries of Kwantung, so the strategic position of Hangu Pass was extremely important, and there was no Tongguan at that time. During the period 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 later the Tong Pass was built, but due to the change of terrain, the Tong Pass lost its effect.
Of course, whether the city gates are dangerous or not depends not only on one aspect, but also on the strength of the state; If the state has collapsed beyond recognition, then it will be difficult to hold the city gates, even if they are no longer dangerous.