The oldest surviving wheel featured a sophisticated axle design to prevent cracking

Discovered in the Ljubljana Marshes of Slovenia, the world's oldest surviving wheel dates to 3200 BC and displays a surprisingly advanced understanding of mechanical stress. Unlike a simple solid disk, which is prone to splitting along the grain, this 120-cm-diameter wheel was constructed from three separate planks of ash wood held together by oak dowels. This tripartite construction allowed the wood to expand and contract without cracking, significantly extending the lifespan of the vehicle.