and historian Joseph Needham writes that what Shen had discovered was Jacob's staff, a surveying tool which was not known in Europe until the medieval French Jewish mathematician Levi ben Gerson (1288–1344) described it in 1321. Jade burial suit: Burial suits made of jade existed in China during the Han Dynasty (202 BC – 220 AD). Confirming ancient records about Han royalty and nobility buried in jade burial suits, archaeologists discovered in June 1968 the tombs and jade burial suits of Prince Liu Sheng (d. 113 BC) and his wife Dou Wan in Hebei province. Liu's suit, in twelve flexible sections, comprised 2,690 square pieces of green jade with holes punctured in the four corners of each piece so that they could be sewn together with gold thread. The total weight of the gold thread used in his suit was 1,110 g (39 oz). Princess Dou Wan's suit had 2,156 pieces of jade stitched together with 703 g (24.7 oz) of gold thread. Although jade burial outer wears and head masks appear in tombs of the early Han Dynasty, burial suits did not appear until the reign of Emperor Wen of Han (r. 180–157 BC), with the earliest being found in the Shizishan site. A total of 22 Western Han (202 BC – 9 AD) and 27 Eastern Han (25–220 AD) complete and partial jade burial suits were uncovered between 1954 and 1996. They are found mainly in Hebei, Shandong, Jiangsu and Henan, as well as at Yangjiawan, Dongyuan, Guangzhou, Mawangdui, Mianyang and Shizhaishan. The jade burial suit gradually disappeared when it was forbidden in 222 by Emperor Wen of Wei. K Keel: Although the keel was a non-Chinese invention, the adjustable centerboard keel traces its roots to the medieval Chinese Song dynasty. Many Song Chinese junk ships had a ballasted and bilge keel that consisted of wooden beams bound together with iron hoops. Maritime technology and the technological know-how allowed Song dynasty ships to be used in naval warfare between the Southern Song Dynasty, the Jin Dynasty, and the Mongols. Kite: As written in the Mozi, the Zhou Dynasty philosopher, carpenter, and structural engineer Lu Ban (fl. 5th century BC) from the State of Lu created a wooden bird that remained flying in the air for three days, essentially a kite; there is written evidence that kites were used as rescue signals when the city of Nanjing was besieged