Tin isotopes reveal changing patterns of tin trade, connectivity and consumption from Anatolia and Central Asia at Kültepe

Until recently, what was known about the trade of tin in the ancient Near East was based in large part on information derived from the extensive commercial archives found at the archaeological site of Kültepe (ancient Kaneš) in Turkey dating to the Middle Bronze Age (MBA) c. 1900-1750 BC. These archives were produced by an expatriate community of traders native to the city of Assur in modern-day Iraq and document an extensive shipping of tin ingots from unnamed sources east of their hometown. Tin was carried by donkeys through northern Syria and across the Taurus Mountains to Anatolia where it was sold for silver.

This paper presents the first set of tin isotope analyses of bronze objects from Kültepe to test the image provided by these ancient archives, finding that all artifacts dated to the main period of Assyrian trade excavated in the residential areas of the site indeed have high tin content and high values of δ¹²⁴Sn (0.77–1.74‰) relative to the NIST 3161a standard. Such high values currently compare best with ores from Central Asia. The isotopic analysis of artifacts from the Assyrian Trading Colony Period of Kültepe is therefore consistent with the textual evidence.

However, Early Bronze Age samples recovered at the site are instead characterized by lower ranges that extend to neutral δ¹²⁴Sn values (0.02–1.31‰). Likewise, one artifact coming from Mound Level 7 (c. 1830-1700) at the center of the site where public buildings were concentrated, and one object dated to the Hellenistic Period (Mound Level 2), when the site saw a resurgence in political importance, likewise have lower δ¹²⁴Sn compositions of 0.11 and 0.31‰, respectively. Both samples also have low to moderate tin content.

The Early Bronze Age artifacts form a linear array between artifacts from low δ¹²⁴Sn-low Sn wt% to high δ¹²⁴Sn-high Sn wt% that suggests a mixing of two compositional groups – not simply the mixing of two isotopically distinct reservoirs of tin, but also distinct in the amount of tin present in the alloy. This would be consistent with the recycling of low tin bronze objects with local tin, together with high tin bronzes containing tin from Central Asia. The two samples from Mound Levels 7 and 2 suggest that although Central Asian tin was predominant in the MBA, Anatolian tin may have continued to be used in a separate bronze production system that remained active at shifting varying of intensity throughout antiquity.