The Silk Road derives its name from the lucrative trade in silk carried out along its length, beginning in the Han dynasty in China (207 BCE–220 CE). The Han dynasty expanded the Central Asian section of the trade routes around 114 BCE through the missions and explorations of the Chinese imperial envoy Zhang Qian, as well as several military conquests. The Chinese took great interest in the security of their trade products, and extended the Great Wall of China to ensure the protection of the trade route.