Guzang, known in ancient times as Wuwei, had been the seat of Liangzhou Prefecture under the previous dynasty.

Eight hundred li west of Guzang stood Yumen Pass.

This pass was the western gateway of the Great Tang, dividing the Central Plains from the Western Regions.

For who knew how many years, it had held back the northern barbarians and suppressed demonic evils. Beneath its walls, the earth had long since been soaked through with blood, black with a purplish cast.