The wheel sounds so obvious that you’d think cave people thought of it. Actually, it took humans a very long time to figure out. The oldest wheel ever found is a wooden disc dug out of a marsh near Ljubljana, Slovenia. Scientists used carbon dating to show it is about 5,150 years old - older than the Egyptian pyramids.
It probably belonged to a small cart. But here’s a twist: people used spinning wheels for making pottery hundreds of years before anyone thought to lay one on its side and roll a load along the ground. Big herds of animals and rough land made carts less useful in many places, so the idea spread slowly.
What’s tricky about a wheel isn’t really the wheel - it’s the axle. The wheel has to spin around a strong, smooth rod while the cart sits on top. Getting that to work without the whole thing wobbling apart took some serious carpentry from our ancient ancestors.
