a time when bows, arrows, and catapult-based projectile launchers were state of the art military technology in medieval Europe. Illustrations and descriptions in the 14th century Chinese military treatise Huolongjing by the Ming dynasty military writer and philosopher Jiao Yu confirm that the Chinese in 1232 used proto-solid propellant rockets then known as "fire arrows" to drive back the Mongols during the Siege of Kaifeng. Each arrow took a primitive form of a simple, solid-propellant rocket tube that was filled gunpowder. One open end allowed the gas to escape and was attached to a long stick that acted as a guidance system for flight direction control. South-pointing chariot: Although the claim of Wei Dynasty mechanical engineer and statesman Ma Jun (fl. 220–265) that the south-pointing chariot was first invented by the mythological Yellow Emperor are dubious, his south-pointing chariot was successfully designed and tested in 255 AD with many later models recreated in subsequent dynasties; this device was a wheeled vehicle with differential gears that ensured a mounted wooden figurine would always point in the southern direction no matter how the vehicle turned, in essence a non-magnetic compass. The Book of Song written in the 6th century states that the device was successfully reinvented by the mathematician and astronomer Zu Chongzhi (429–500) during the Liu Song Dynasty (420–479). The Japanese historical text Nihon Shoki, compiled by 720, states that the device was crafted and presented as a gift to Emperor Tenji (661–672) on two different occasions (658 and 666) by the Tang Dynasty (618–907) Chinese Buddhist monks Zhi Yu and Zhi You. The wheeled vehicle device was described in intricate detail in the historical text covering the Song Dynasty (960–1279), i.e. the Song Shi (compiled 1345); for example, it revealed the number of gear teeth on each mechanical gear wheel, the diameter of each gear wheel, and how these gear wheels were properly positioned. Soybean oil: Chinese records dating prior to 2000 BC mention the use of cultivated soybeans to produce edible soy oil. Ancient Chinese literature reveals that soybeans were extensively cultivated and highly valued as a use for the soybean oil production process before written records were kept. Soy sauce: Soy sauce in its current form was created about 2,200 years ago during the Western Han dynasty and was soon spread throughout East and Southeast Asia where it is used in cooking and as a condiment. The condiment