How to understand the meaning of "Ba and Shu are dangerous, and everyone who moved from Qin lived in Shu"

"Ba, Shu road is dangerous, and all the people who moved from Qin lived in Shu" means that the roads in Cuba and ancient Shu are steep, and all the people who moved from Qin lived in Shu.

from the biography of Han Xiao He and Cao Can.

The Book of Hanshu, also known as the Book of Pre-Hanshu, was compiled by Ban Gu, a historian in the Eastern Han Dynasty in China. It lasted for more than 2 years, and was basically completed in Jianshe Junior High School, and was annotated by Yan Shigu in the Tang Dynasty. It is the first biographical dynastic history in China, one of the "Twenty-four History".