1, fertile soil
In ancient times, the most important criterion to evaluate whether a place is suitable for human habitation is whether the soil in this place is fertile or not, because food is the most important thing for people. If the soil in this place is not good and it is not suitable for growing crops, even if the scenery here is good, it cannot be called a good place.
Sichuan basin belongs to subtropical monsoon humid climate, which is suitable for crop growth. In addition, Li Bing dug Dujiangyan, which made the irrigation system in Sichuan Basin extremely developed, so the general drought did not affect the Sichuan Basin at all, so the Sichuan Basin often harvested crops year after year.
In ancient times, if a place was not short of food or food, it was naturally a land of abundance. Zhuge Liang once said, "Yizhou is in danger, fertile fields are thousands of miles away, and the land of abundance is rich, so the emperor can become an emperor." Many dynasties in the history of China regarded Sichuan as an important grain tax place.
2, easy to defend but difficult to attack
In ancient times, Sichuan had inconvenient transportation, and it was easy to defend but difficult to attack. Li Bai once wrote a poem, "It is difficult to get through the road, but it is difficult to go to the sky." From the perspective of modern people, it is natural that the more convenient the transportation, the better, but this was not the case in ancient times, at least not completely.
In ancient times, it was easy to have unrest in case of natural and man-made disasters. As for dynasty change, the unrest was even more extensive. However, Sichuan is rarely affected by the turmoil, because Sichuan is surrounded by mountains, though Dagger-Tower Pass be firm and grim, and it is difficult for outsiders to break into Sichuan. As long as Sichuan strictly abides by the pass, it can be guaranteed to be safe. Therefore, Sichuan has become more and more prosperous, and finally surpassed other rich areas and became a land of abundance recognized by everyone.
Topography of Sichuan
Sichuan Province is located in the first and second steps of Chinese mainland's terrain, that is, in the transition zone between the first Qinghai-Tibet Plateau and the third Yangtze River plain, with great disparity in height, and the characteristics of high in the west and low in the east are particularly obvious. The western part is plateau and mountain, with an altitude of more than 3000 meters; There are basins and hills in the east, and the elevation is mostly between 500 and 2000 meters. The whole province can be divided into five parts: Sichuan Basin, Western Sichuan Alpine Plateau, Northwest Sichuan Hilly Plateau, Southwest Sichuan Mountain and Micang Mountain Daba Mountain.
The landform of Sichuan is complex, with mountains as the main feature. There are four types of landforms, namely, mountains, hills, plains and plateaus, accounting for 74.2%, 10.3%, 8.2% and 7.3% of the total area of the province respectively. There are 25 soil types, 63 subclasses, 137 soil genera and 380 soil types, accounting for 43.48% and 32.60% of the national total respectively.
Reference to the above content: Baidu Encyclopedia-Sichuan