Due to the changes over time, the current terrain is completely different from ancient times, so it is sometimes difficult to imagine why "one man can hold the pass."

During the Qin Dynasty, the Earth's temperature was higher, and the primeval forest was dense, making it impassable for ancient armies. There were only three passages into the Qin state from the Central Plains. Crossing the Yellow River to attack the Qin state from the north was difficult at that time.

The Wuguan in the south was either a detour or, like the Hangu Pass, was also easy to defend and difficult to attack.

The central Hangu Pass is a crack between two mountains, covered with primeval forests. The pass was built outside the crack, and to attack it, one had to cross the Hongnong River, further increasing the difficulty of attack.

Therefore, the Qin state first spent many generations fighting against the Jin and Wei states, obtaining the Hangu Pass and the "Hexi Land" to its west. Only then did they face the danger of the Hangu Pass. In addition, the Sichuan Basin was transformed into the "Land of Abundance" using the Dujiangyan Irrigation System, taking advantage of the favorable geographical and climatic conditions.

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