Hanguguan, Ci Hai explained: "Because it is locked in the valley, it is as dangerous as a letter, hence the name. It starts from Lushan Mountain in the east, reaches Jintong in the west, and leads to Hangu, which is known as the natural barrier. " A letter refers to a box or lid for holding things, which is deep and closed. According to the general theory of archaeology, "Guansai began in Yin. Zhou called the peach forest land a peach forest plug. Zhou Wuwang attacked Yin, imperial edict was sent to Hangu Pass, governors were there, merchants were doing business, and cattle herding was in Taolin, that is, a "risk management" was set up, and Taolin has become a pass ... "It can be seen that Hangu Pass was built at the beginning of the week. Hanguguan, "There are plateaus in the west, Juejian in the east, Qinling in the south and Yellow River in the north". The road is in the deep valley, but things are a hundred miles away. "The horse does not converge, and the car has no trace." The two walls are steep and the trees cover the sky. It can be said that "one person guards them, and ten thousand people cannot force them." It is an important military fortress in ancient times and a battleground for military strategists. There have been many influential wars here in history. For example: Guo Gong was humiliated. In 658 BC, Jin Xiangong bribed Quan Rong, who lived in Lishan Mountain, to attack Guo from the west, and Quan Rong's soldiers went to Sangtian (now Housang Village, Hanguguan Town). Guo Gong led an ambush from both sides of the ancient Hangu road, commanding, and Quan Rong fled in defeat. Five vertical attacks on Qin. In 3 18 BC, Chu, Zhao, Wei, Han and Yan elected Chu Huaiwang as the king of Qin, and they jointly attacked Qin for the first time. The allied forces attacked Hangu Pass and were repelled by Qin Jun. "All the divisions of the five countries were defeated"; Chu and Han fought for customs. In 206 BC, Liu Bang took the lead in attacking Wuguan to destroy Qin, and also defended Hanguguan to repel Xiang Yu. In the battle between the two armies, Xiang Yu finally broke through and settled in Hongmen. Nishihara War. In 756 AD, General Ge of the Tang Dynasty attacked Xiyuan (the former site of Hangu Guanxi) in the Anshi Rebellion. Tang Jun was lured into Hangu Pass, and was ambushed and attacked by fire. In War of Resistance against Japanese Aggression, Hangu Pass also played an important role. 1April 944, only a few Japanese troops launched the "Henan Battle". In just over 20 days, they captured Lingbao County from Luoyang (Zaoling Town, Dawang, the bank of the Yellow River in the northwest of the old city, which has been submerged by Sanmenxia Reservoir). China's army defended Hanguguan and Henglingyuan, hitting the Japanese army hard, killing and injuring more than 2,000 Japanese captains and heads. A small number of Japanese troops fled to Kanxiang and immediately retreated, but failed to advance further westward. Throughout the ages, Hanguguan is the only place to connect Qin and Yu, and many famous writers have left legends and famous sentences here. Allusions such as "a white horse is not a horse", "the final army abandons the body", "crowing dogs and thieves" and "purple gas coming from the east" all happened here. From the Han Dynasty to the Ming and Qing Dynasties, hundreds of poems about Hanguguan have been handed down, including the poems of Li Shimin, Li Longji and Yang Yuhuan, as well as the masterpieces of Li Bai, Du Fu, Bai Juyi, Liu Yuxi, Han Yu, Wei, Yuan Haowen and Li Qingzhaohe. The most famous is Lao Kun, who rode a green cow across Hangukou. At the invitation of Guan Lingyin Xi, he wrote China's earliest philosophical work, Tao Te Ching, which is 5000 words long. Later, the Tao Te Ching was regarded as a classic by Taoism, and Hanguguan became a sacred place for Taoist believers to worship their ancestors. The letter valley pass mentioned above is the ancient letter valley pass, also called Qin letter valley pass. In addition, there are two places called Hangukou, one is Weihangukou, which is on the bank of the Yellow River about ten miles north of Qinhanggukou. According to historical records, in the 16th year of Jian 'an of Emperor Xian of Han Dynasty (AD 2 1 1), Cao Cao made a westward expedition to Zhang Lu and Ma Chao, which promoted agriculture. Seeing that the Hanguguan ancient road was rugged and difficult to transport grain and grass, General Chu Xu was ordered to open up a new road on the bank of the Yellow River, which was the "Cao Cao's Road to Transport Grain". In the first year of Wei Zhengshi (AD 240), Meng Kang, the magistrate of Hongnong, built a new Guancheng at the entrance of the main road of grain transportation, named Daguguan, also known as Jindou Pass, and later called Hanwei Valley Pass. The closed building of this pass was destroyed during the War of Resistance against Japanese Aggression period. Another Hangu Pass is located in Dongyihuali, Xin 'an County. It is called Hanguguan, also called Xinhuguan, which was built by Yang Fu, a ship general during the reign of Emperor Wu of the Han Dynasty. At that time, the capital was in Chang 'an, and people were proud of living in Guan and ashamed of living outside. Yang Fu was from Yiyang (Yiyang belonged to Xin 'an at that time) and was ashamed of being a foreigner. He wrote to Emperor Wu of the Han Dynasty, and in three years (A.D. 1 14), he donated all his family wealth and moved Hanguguan to Xin 'an. This building still exists.