 Furthermore, the Song employed the earliest known gunpowder-propelled rockets in warfare during the late 13th century, its earliest form being the archaic Fire Arrow.When the Northern Song capital of Kaifeng fell to the Jurchens in 1126, it was written by Xia Shaozeng that 20,000 fire arrows were handed over to the Jurchens in their conquest.An even earlier Chinese text of the "Wujing Zongyao" ("Collection of the Most Important Military Techniques"), written in 1044 by the Song scholars Zeng Kongliang and Yang Weide, described the use of three spring or triple bow arcuballista that fired arrow bolts holding gunpowder packets near the head of the arrow.