From diversity to monopoly: major economic policy change in the Western Han Dynasty revealed by lead isotopic analysis

The relationship between the flow of metal and the state political and economic structures of the Qin and Han empires has thus far received inadequate scientific investigation. In this study, lead isotopic analysis was conducted on 54 bronzes unearthed from multiple sites of Eastern China dated to WHD (Western Han Dynasty: 202 BC-AD 23), including containers, chariot and horse gears, weapons, mirrors, coin moulds, coins, and weighing and measuring instruments. The provenance of lead-bearing materials is a vital question. The current results indicate no noticeable regional variations, all falling into the traditionally known category of common lead. However, the variation in lead isotope becomes increasingly narrow from the early to late WHD. The lead sources during the early WHD were much complicated, but those used in the middle to late WHD were more uniform and broadly consistent with the minerals used in WHD mirrors from Chang’an and Japan, most likely from the western Henan area. To stabilize the economy and fight against the Xiongnu, Emperor Wu decided to nationalize the trade of salt and iron. Consequently, local mining and casting of bronzes were also banned, forcing bronze material from different regions to be concentrated in a few metropolitan centres. The shift in the WHD’s economic strategy from free operation to state monopoly has been crystalized in the lead isotopes.