Volume 5, Chapter 27: Scattered, Vivid Shadows of Apricot Blossoms

On the seventh day of the fourth month, the Yong army fled in disarray. Their retreat path was blocked by the light cavalry of the Daizhou army, while Long Tingfei pursued doggedly on their heels until reaching the border between Qin and Ze. As the two armies were consumed by battle, the Yong army’s ambush poured out. On the Yong Emperor’s orders, Zhangsun Ji had hidden all traces of their presence, including his marshal’s banner, as he laid in ambush for several days. Three hundred sixty thousand Yong troops trapped the Northern Han army in the wilderness.

—Zizhi Tongjian, Yong Records Volume Three