"Forty-eight thousand years have passed without communication with Qin Sai" comes from Li Bai's "Difficult Road to Shu", which means that since then, Qin Shu has been cut off by the Qinling Mountains for about 48 thousand years, referring to the Sichuan Basin on the south side of the Qinling Mountains. Sichuan Basin borders Qinghai-Tibet Plateau and Hengduan Mountains in the west, Qinling and Loess Plateau in the north, Xiangxi and Hubei Mountains in the east and Yunnan-Guizhou Plateau in the south.
Shu Road, the road from Chang 'an to Shu in ancient times, passes through Qinling and Daba Mountains, with high mountains and deep valleys, rugged roads and difficult access. From Guanzhong to Hanzhong, it is composed of Praise Road, Ziwu Road, Chencang Road and Luo Luo Lu, and from Hanzhong to Chengdu, Sichuan, it is composed of Jinniu Road, Micang Road and Litchi Road. "Dragon Tree in the North of Zhan Ge" depicts the land traffic scene of ancient Qin and Shu.
The difficulty of Shu Dao is an old topic in Yuefu, which belongs to the title of Harmony Songs and Tones, and most of them describe the difficulties of Shu Dao. Before the Tang Dynasty, Liang Jianwen, the second emperor of the Southern Liang Dynasty in the Northern and Southern Dynasties, and Liu Xiaowei, a poet in the Southern Dynasties, each wrote two poems, and Yin Keng wrote one. However, Li Bai, a poet in the prosperous Tang Dynasty, wrote Shu Dao Nan to the end.
Overall form:
The outline of Sichuan basin is generally approximate to a rectangle, shaped like an envelope and inclined to the right on the Asian continent, so it is called an envelope basin by geographers. Yunyang in the east (near Wanzhou), Xuyong in the south (near Zunyi), Ya 'an in the west, and Guangyuan in the north of the envelope basin.
The geometric center city of the envelope basin is Suining (the geometric center point is roughly in the south of Pengxi), Nanchong (the inner corner) in the north-central part, and Anyue in the south-central part.