How mant years did it take Zhang Qian to complete his diplomatic mission albeit unsuccessfully

Today Zhang Qian's travels are associated with the major route of transcontinental trade, the Silk Road. In essence, his missions opened up to China the many kingdoms and products of a part of the world then unknown to the Chinese. Zhang Qian's accounts of his explorations of Central Asia are detailed in the Early Han historical chronicles, Records of the Grand Historian, compiled by Sima Qian in the 1st century BC. The Central Asian sections of the Silk Road routes were expanded around 114 BC largely through the missions and explorations of Zhang Qian. [2] Today Zhang Qian is considered a national hero and revered for the key role he played in opening China to the world of commercial trade.