Geometric morphometric analysis sheds new light on silver bullion production systems of the Southern Song period

The Song Dynasty marked a pivotal moment in Chinese fiscal history by establishing the first monetized taxation system. By the Southern Song period (1127–1279), silver became deeply integrated into this system, and gradually supplanted iron and copper coins as the standard measure of value for paper money. Archaeological findings frequently uncover tax silver in the form of silver bullions, which played a significant role in the payment and transportation of tributes and taxes from local to central governments. The study of these bullions offers valuable insights into the taxation and economic history of China's first silver-based taxation system. While prior research has extensively examined the inscriptions on silver bullions, their morphological characteristics have received comparatively little attention. This study analyses the orthoimages of 113 Southern Song silver bullions to investigate potential correlations between their shapes and the production systems of the time. By employing a quantitative analysis of silver bullion outlines using two-dimensional geometric morphometric methods (2D-GMM) based on Elliptic Fourier Analysis and multivariate statistical techniques, the research reveals that the shapes of silver bullions vary with their weights and production locales, indicating a de-centralized bullion production system involving numerous prefecture level governments. Notably, a substantial number of silver bullions produced by gold and silver shops exhibit highly consistent shapes, although each shop had its own workshop and some of them were geographically distant from each other. Frequent exchanges between vouchers of monopolized products and silver bullions at these shops likely contributed to a high uniformity of bullion shapes. By integrating quantitative methods, this research provides a novel perspective on the study of Southern Song silver bullions and offers new insights into the silver-based taxation system during this period.