In A.D. 1044, the complicated preparation method of gunpowder was recorded in the military work Wu Yao written by people in the Northern Song Dynasty. In the Yuan Dynasty, it further developed into a metal vessel, that is, artillery. The bronze gun of the 3rd year of Shunzhi (A.D. 1332), now in the Chinese History Museum in Beijing, is the earliest existing metal gun in the world. It weighs 6,94kg, is 35,3cm long, and has a diameter of 10.5cm. The middle cover of the barrel is engraved with "February 14th, the 3rd year of Shunzhi".