The geographical environment of Luoyang determines that Luoyang is one of the first choices for the capital of ancient great dynasties. Luoyang is located in the transitional zone between the Central Plains, the western mountainous area and the eastern plain. To the north of Luoyang is the Yellow River, and Luoshui passes through the south of the city. Yishui is also close to Luoyang, and the water source problem can be solved. In addition, there are Mangshan Mountain in the north, Songshan Mountain in the east and hills and Xiong 'er Mountain in the southwest. The history book says that "Luoyang controls mountains and rivers, which is really the best in the world."
Specific to four levels, let's talk about executives first. Speaking of executives, you may not be familiar with them. Liu Guan in The Romance of The Three Kingdoms and Hulao Pass of Lu Bu are actually Guan. In addition, the elevation also has a famous name-Sishuiguan. Hulao Pass is located on the south bank of the Yellow River and the west bank of Surabaya, with a triangular trend. From Hulao Pass to Luoyang in the west, there are about hundreds of miles, and with the barrier of Luoshui, as long as we hold Luoshui, the eastern line of Luoyang will be safe.
At the end of the Eastern Han Dynasty, Dong Zhuo occupied Luoyang, and Yuan Shao and others were afraid of Dong Zhuo and did not dare to invade. Only Cao Cao marched westward with his own military forces, ready to occupy Hulao Pass. Cao Cao thought that as long as Hulao Pass was captured, there would be no danger to the east of Luoshui. After Luoshui, Luoyang is also in danger. In 423 AD, the Northern Wei army captured Luoyang, and at the same time, Wei Jun also attacked Tiger Prison. In the Northern Wei Dynasty and the early Ming Dynasty, Yuan Di Tuoba Si personally attacked Hulao Pass and paid a huge price to win it. Ren Wei knows very well that if you take the Tiger Prison, there will be danger to the east of Luoyang. The tiger prison is in the hands of the Song Dynasty, and Luoyang can't keep it sooner or later.
To the west of Luoyang is Hangukou, which seems to be quite famous. The so-called Kanto and Kansai in the pre-Qin and Han dynasties were actually bounded by Hangu Pass. However, it should be noted that there were three Hangu Pass in Qin, Han, Wei and Jin Dynasties. The earliest Hangu Pass in Qin Dynasty was located in lingbao city, which is under the jurisdiction of Sanmenxia City, Henan Province. Hangu Pass in Han Dynasty is about150km east of Hangu Pass in Qin Dynasty. There is also the Hangu Pass built by Cao Cao, which is also in Lingbao. Generally speaking, Hangu Pass refers to Lingbao's Hangu Pass in Qin Dynasty. But no matter which Hangu Pass is located in the west of Luoyang, it is of great significance to Luoyang's western defense.
Southwest of Luoyang is a Queguan, which is not very famous. But there is a mountain next to yique, called Longmen mountain, and there is a grotto on Longmen mountain, called Longmen grottoes. The world-famous Longmen Grottoes, also known as Yi Que Grottoes. The terrain of yique is very dangerous. It spans the banks of Yishui, with Longmen Mountain in the west and Xiangshan in the east. By the way, this poem "Xiangshan" by Bai Juyi, a Buddhist in Xiangshan, is here. If the enemy attacks yique from the southern line to the north, after taking yique, they can go north along Yishui to Luoshui, with Luoyang city on the north bank of Luoshui.
Jin Meng is also the "Shuiguan", located on the south bank of the Yellow River, more than ten kilometers northeast of Luoyang City in the Eastern Han Dynasty, and at the northern foot of Mangshan Mountain. Since ancient times, it has been an important town for defending the northern line of Luoyang. Since Cao Cao's separatist regime in the Central Plains, in order to defend the northern enemy from going south, it is necessary to assemble heavy troops in Jin Meng. Since the Eastern Han Dynasty, Cao Wei, the Western Jin Dynasty, the Northern Wei Dynasty (later period), the Sui Dynasty (Yang Di moved its capital), the Tang Dynasty (the eastern capital, the divine capital) and the later Tang Dynasty all took Luoyang as their capital, and Jinmengguan was just like the North Gate for these dynasties. If the North Gate is opened, whether you are Wei Mingdi or Sima Yan, Yang Di or Wu Zetian, you will break out in a cold sweat. Even if it is not the Central Plains dynasty with Luoyang as its capital, such as the five dynasties of Liang, Jin, Han, Zhou, Northern Song and Jin (later period), Kaifeng will still open if Luoyang can't hold on. Therefore, defending Jinmengguan is also the top priority of the northern defense system of these dynasties with Kaifeng as the capital.
Luoyang has the risk of four passes, which is easier to defend than Kaifeng in the plain. Kaifeng is too peaceful to defend. Zhang Yi of Qin once said: The girder (Kaifeng) has a flat terrain, which can pass through the world, and it is more suitable for fighting without the danger of famous mountains and rivers. In the Northern Song Dynasty, Zhao Kuangyin planned to move the capital to Luoyang, because Kaifeng was difficult to keep, and Luoyang was at least in danger of mountains and rivers. If the capital is moved to Luoyang, there will be no need for so many troops to stick to Kaifeng, resulting in the cost of "redundant soldiers".
During the reign of Injong, Minister Fan Zhongyan discussed with Lv Yijian about moving the capital. Fan Zhongyan's attitude is: Luoyang has solid rivers and mountains, and Kaifeng is too low and peaceful. If it is peacetime, Kaifeng can be its capital. Once something happens in the world, moving the capital to Luoyang is the best policy. Although Luoyang was not the official capital of the Five Dynasties and the Northern Song Dynasty, it was always built by Xijing and was an important link in the defense system of the dynasties along the Yellow River.