of Chibi in 208 AD, the Prime Minister Cao Cao once linked the majority of his fleet together with iron chains, which proved to be a fatal mistake once he was thwarted with a fire attack by Sun Quan's fleet. The armies of Emperor Taizu of Song had a large pontoon bridge built across the Yangtze River in 974 in order to secure supply lines during the Song Dynasty's conquest of the Southern Tang. Porcelain: Although glazed ceramics existed beforehand, the author and historian Samuel Adrian M Adshead writes that the earliest type of vitrified, translucent ceramics that could be classified as true porcelain was not made until the Tang Dynasty (618–907). The archaeologist Nigel Wood of the University of Oxford states that true porcelain was manufactured in northern China from roughly the beginning of the Tang Dynasty in the 7th century, while true porcelain was not manufactured in southern China until about 300 years later, during the early 10th century. Pound lock: Indirect evidence suggests that pound locks may have been used in antiquity by the Ptolemaic Greeks and the Romans. In China, although the one gate canal flash lock existed beforehand, the two-gate pound lock was invented in 984 by an official of Huainan and engineer named Qiao Weiyo, during the early Song Dynasty (960–1279), so that ships could safely travel along canal waterways having gated and segmented chambers where water levels could be regulated. The economic and transport benefits of this innovation were described by the polymath official and inventor Shen Kuo (1031–1095) in his Dream Pool Essays. Puddling process: The puddling process was known the ancient Chinese during the Han Dynasty by the 1st century AD. The improvement of steelmaking processes improved the overall quality of steel by repeated forging, folding, and stacking of wrought iron from pig iron to make swords. Puppet theater, waterwheel-powered: The mechanical toys of Roman Egypt, especially the weight-driven puppet theater of Heron of Alexandria (c. 10–70 AD), are well known and discussed by historians such as Beck, Prou, and de Rochas d'Aiglun. In China, Zhang Heng (78–139) wrote of plays with artificial fish and dragons, while a 6th-century text Xijing Zaji states that when Liu Bang (reigned as Emperor Gaozu of Han from 202–195 BC) came upon the treasury of the deceased Qin Shihuang (r. 221–210) in 206 BC, he found an entire mechanical orchestra of 1 m (3 ft)