An engineering investigation on the Bronze Age crossbar wheel of Mercurago

The Bronze Age crossbar wheel found in the XIX century in Mercurago (Italy) is an amazing example of the technical innovations stimulated by the diffusion of horse draught war chariots in Europe across the third and second millennium B.C. It is a tripartite wheel, with two felloes attached to a diametric crossbar by means of internal dowels, and four thinner rods departing from the crossbar near the hub and ending into the felloes. A separate nave is inserted into the crossbar hub. Many question are still open about this wheel, concerning in particular its constructive concept, the materials and the role of each member. In this paper the tools of modern engineering, in particular the laser-scanner acquisition technology and the finite element method, were used to study the structural issues concerning the crossbar Mercurago wheel under the hypothesized operating conditions. Verisimilar explanations of some technical choices, such as the shape and the materials of the members, were obtained; furthermore, the presence of a leather tire was hypothesized on the basis of the rim-soil contact analysis. Finally, the role of the inserted nave was investigated. It was hypothesized that it could have a role similar to modern bushings, thus being a very innovative device for that time.