Metallurgical investigation on bronze artillery projectiles of Susa, Southwestern Iran

Abstract Bronze projectiles represent an important class of artefacts in the archaeology of the ancient Near East, particularly for the study of warfare and military organization. Although they are less effective than ceramics for precise chronological attribution, their abundance, standardized forms, and high mobility make them valuable indicators of conflict-related activities, siege warfare, and the logistical organization of armies. Large assemblages of projectiles allow for comparative technological studies, while their mobility provides insights into weapon circulation and raw material procurement networks. A group of morphologically identical bronze projectiles was recovered from Susa during Iranian archaeological campaigns conducted between 1982 and 2005. These artefacts were excavated by Mir Abedine Kaboli from the western retaining wall of the Apadana Tepe, a context that strongly suggests a military function, possibly related to siege or defensive activities. The standardized appearance of the objects raises important questions regarding their production technology, material sourcing, and the organization of weapon manufacture. Copper-based artefacts are particularly informative archaeological materials, as their chemical composition, microstructure, and corrosion features preserve long-term evidence of metallurgical practices and technological choices. Archaeometallurgical approaches provide a framework for reconstructing alloy selection, casting techniques, and supply systems, thereby contributing to broader discussions on craft specialization, trade networks, and military logistics. This study aims to investigate the production and supply strategies behind these bronze projectiles through a combined analytical approach. Lead isotope analysis (LIA) was employed to identify the provenance of lead used in the alloys, while XRF and SEM–EDS analyses, supported by reflected-light optical microscopy, were used to characterize alloy composition and microstructural features. Together, these methods enable the assessment of both raw material sources and manufacturing techniques. The results indicate that most of the analysed projectiles are leaded tin bronzes with relatively standardized alloy compositions, suggesting controlled and possibly centralized production. However, lead isotope data reveal a strong correlation between the lead component and ore sources from the Pontic Black Sea region. This evidence points to long-distance procurement of raw materials and highlights the complexity of metallurgical supply networks involved in the production of military equipment during this period.