Established by Shi Huangdi, it originally covered the entire territory of the Qin Empire west of Mount Long with its seat at Didao (present-day Taoyang in Lintao County).
Its principal route of communication was the Long Road (named for the mountain), which probably passed along the course of the modern railroad west from Xi'an although much of the area nearest the river was then marshland.
The Emperor Wu of the Han dynasty, as part of his expeditions into the Tarim Basin, established Tianshui Commandery to control the Wei valley immediately to the west of Mount Long.
The remnant of Longxi controlled eleven counties in the far west of the Wei and the Tao valley.
The entry to the lower Wei was removed from the valley itself to the then-forested loess foothills north of Mount Long.