theaters; this along with traveling foreigners and Chinese who migrated to urban centers from regions with different cooking styles encouraged a demand for a variety of flavors served at urban restaurants, giving rise to the menu. Revolving bookcase: Revolving bookcases, known as zhuanluntang, have been documented in ancient China, and its invention is credited to Fu Xi in 544. Descriptions of revolving bookcases have been found in 8th- and 9th-century Chinese texts. Revolving bookcases were popularized in Buddhist monasteries during the Song Dynasty under the reign of Emperor Taizu, who ordered the mass printing of the Buddhist Tripiṭaka scriptures. An illustration of a revolving bookcase is depicted in Li Jie's architectural treatise the Yingzao Fashi. Rockets: The first gunpowder-powered rockets were developed during the Song dynasty and by the 13th century. The Chinese rocket technology was adopted by the Mongols and the invention was spread via the Mongol invasions to the Middle East and Europe in the mid-13th century. Rockets are recorded to have been used by the Song navy in a military exercise dated to 1245. Internal-combustion rocket propulsion is mentioned in a reference to 1264, recording that the 'ground-rat,' a type of firework, had frightened the Empress-Mother Gongsheng at a feast held in her honor by her son the Emperor Lizong. Subsequently, rockets are included in the military treatise Huolongjing, also known as the Fire Drake Manual, written by the Chinese artillery officer Jiao Yu in the mid-14th century. This text mentions the first known multistage rocket, the 'fire-dragon issuing from the water' (huo long chu shui), thought to have been used by the Chinese navy. Rocket bombs, aerodynamic wings and explosive payloads: The first known rockets fitted with aerodynamic wings are described as the 'flying crows with magic fire' in the oldest strata of the Huolongjing (early-to-mid 14th century), compiled by Jiao Yu and Liu Bowen during the early Ming Dynasty (1368–1644). The body of the rocket was shaped like a bird (specifically a crow), packed with gunpowder, and made of bamboo laths forming a long basketwork frame that was reinforced with glued paper. A decorative head and tail were attached to the front and back ends, while the wings were nailed to the sides. Under each wing were two slanting rockets to propel the weapon; a main fuse was lit that ignited a fourfold fuse connected to each rocket and running through a drilled hole in