<Li> Color printing: By at least the Yuan Dynasty, China had invented color printing for paper . British art historian Michael Sullivan writes that "the earliest color printing known in China, and indeed in the whole world, is a two - color frontispiece to a Buddhist sutra scroll, dated 1346". </Li> <Li> Contour canal: After numerous conquests and consolidation of his empire, China's first emperor Qin Shi Huang (r . 221--210 BC) commissioned the engineer Shi Lu to build a new waterway canal which would pass through a mountain range and connect the Xiang and Lijiang rivers . The result of this project was the Lingqu Canal, complete with thirty - six lock gates, and since it closely follows a contour line (i.e. following the contours of the natural saddle in the hills), it is the oldest known contour canal in the world . </Li> <Li> Counting rods: Counting rods were used by ancient Chinese for more than two thousand years . In 1954, forty - odd counting rods of the Warring States period were found in Zuǒjiāgōngshān (左 家 公 山) Chu Grave No. 15 in Changsha, Hunan . In 1973, archeologists unearthed a number of wood scripts from a Han dynasty tomb in Hubei . On one of the wooden scripts was written: "当 利 二 月 定 算". This is one of the earliest examples of using counting rod numerals in writing . In 1976, a bundle of Western Han counting rods made of bones was unearthed from Qianyang County in Shaanxi . The use of counting rods must predate it; Laozi (6th or 5th century BCE) said "a good calculator doesn't use counting rods". The Book of Han recorded: "they calculate with bamboo, diameter one fen, length six cun, arranged into a hexagonal bundle of two hundred seventy one pieces". At first calculating rods were round in cross section, but by the time of the Sui dynasty triangular rods were used to represent positive numbers and rectangular rods were used for negative numbers . </Li> <Li> Crossbow and repeating crossbow: According to British art historian Matthew Landruss and Gerald Hurley, Chinese crossbows may have been invented as far back as 2000 BC, while Anne McCants speculates that they existed around 1200 BC . In China bronze crossbow bolts dating as early as the mid 5th century BC were found at a State of Chu burial site in Yutaishan, Hubei . The earliest handheld crossbow stocks with bronze trigger, dating from the 6th century BC, comes from Tomb 3 and 12 found at Qufu, Shandong, capital of the State of Lu . Other early finds of crossbows were discovered in Tomb 138 at Saobatang, Hunan dated to the mid 4th century BC . Repeating crossbows, first mentioned in the Records of the Three Kingdoms, were discovered in 1986 in Tomb 47 at Qinjiazui, Hubei dated to around the 4th century BC . The earliest textual evidence of the handheld crossbow used in battle dates to the 4th century BC . Handheld crossbows with complex bronze trigger mechanisms have also been found with the Terracotta Army in the tomb of Qin Shihuang (r . 221--210 BC) that are similar to specimens from the subsequent Han Dynasty (202 BC--220 AD), while crossbowmen described in the Han Dynasty learned drill formations, some were even mounted as cavalry units, and Han dynasty writers attributed the success of numerous battles against the Xiongnu to massed crossbow fire . In comparison, the ancient Greeks also had a crossbow known as the gastraphetes ("belly - bow", so named because the shooter had to draw the bow by pressing his stomach against the concave rear) also invented in the 5th century BC; other versions were the more portable Cheirobalista (hand balista), arcubalista and manubalista, this last Roman version was almost all metal composed (the spring mechanism and the skeins). There was also the katapeltikon (399 BC), a siege weapon using similar mechanisms . Unlike the Chinese crossbow, the heavy weight and bulk of these weapons necessitated a prop to keep them standing . </Li>

List three important technological innovations that came out of tang dynasty china