It is said there were two books on the art of war by Wu Qi, but one was lost, hence leaving the "Wuzi" as the only existing book carrying Wu Qi's military thoughts. The oldest "Wuzi" edition that survives dates to the Song Dynasty (960–1279). Because of the lack of surviving copies, there is no consensus among modern scholars concerning the latest date of the "Wuzi"'s final composition, but the core of the work is nominally assumed to have been composed around Wu Qi's lifetime (440–381 BC), in the mid-Warring States period. Historical references indicate that the "Wuzi" was very famous and popular in both the Warring States period and in the Han dynasty. In addition to strategic/tactical studies and the philosophy of war, the "Wuzi" pays significant attention to the logistical achievement of war preparedness.