The Silk Roads' origin lay in the hands of the Chinese. The soil in China lacked Selenium, a deficiency which contributed to muscular weakness and reduced growth in horses. Consequently, horses in China were too frail to support the weight of a Chinese soldier. The Chinese needed the superior horses that nomads bred on the Eurasian steppes, and nomads wanted things only agricultural societies produced, such as grain and silk. Even after the construction of the Great Wall, nomads gathered at the gates of the wall to exchange. Soldiers sent to guard the wall were often paid in silk which they traded with the nomads. Past its inception, the Chinese continued to dominate the Silk Roads, a process which was accelerated when "China snatched control of the Silk Road from the Hsiung-nu" and the Chinese general Cheng Ki "installed himself as protector of the Tarim at Wu-lei, situated between Kara Shahr and Kucha." "China's control of the Silk Road at the time of the later Han, by ensuring the freedom of transcontinental trade along the double chain of oases north and south of the Tarim, favoured the dissemination of Buddhism in the river basin, and with it Indian literature and Hellenistic art."