A Late Bronze Age tin ingot from Sursee-Gammainseli (Kt. Luzern)

Abstract

The small island of Gammainseli is situated in the central Swiss Lake Sempachersee near the town Sursee (Kt. Luzern). The multi-phase, partly submerged site includes layers from the Neolithic and the Late Bronze Age. The Neolithic occupation is still undated. Dendrochronological analysis indicates three Bronze Age settlement phases dating to the late 11th, the 10th and the early 9th centuries BC. During submarine surveys in the still unexcavated site, a tin ingot, as well as a few pottery sherds were found on the lake floor. The ingot contains relatively pure tin containing 1.5 % of lead and thus remarkably high content of this metal. Although metallurgical and lead isotope analyses were conducted it was not possible to determine the origin of the metal with certainty. It is most likely that the ingot was imported from the Erzgebirge area on the German-Czech border. Whether the lead is a natural part of the tin or it was added on purpose remains uncertain. Parts of the ingot had been removed for the purpose of bronze production. The original weight must have been approx. 700 g. Artefacts made of tin, ceramics with tin foil ornaments as well as unworked fragments are known from Late Bronze Age sites in Switzerland. Wires, small bars and melted drops of tin are found in a number of Swiss sites, and are interpreted as raw material and as remains of the bronze production. Consequently, tin was used in the settlements, and imported as a pure metal. A few finds of copper ingots also prove the local production of bronze. Hoards containing bronze scrap as well as bronze ingots indicate trade with alloyed metal.