Hugh Pickens writes writes: "Wheels are the archetype of a primitive, caveman-level technology and we tend to think that inventing the wheel was the number one item on man's to-do list after learning to walk upright, but LiveScience reports that it took until the bronze age (3500 BC), when humans were already casting metal alloys and constructing canals and sailboats, for someone to invent the wheel-and-axle, a task so challenging archeologists say it probably happened only once, in one place. The tricky thing about the wheel isn't a cylinder rolling on its edge but figuring out how to connect a stable, stationary platform to that cylinder. "The stroke of brilliance was the wheel-and-axle concept," says David Anthony, author of "The Horse, the Wheel, and Language." To make a fixed axle with revolving wheels, the ends of the axle have to be nearly perfectly smooth and round, as did the holes in the center of the wheels and the axles have to fit snugly inside the wheels' holes, but not too snug or there will be too much friction for the wheels to turn. Another issue is the size of the axle because while a thin one will reduce the amount of friction, it will be too weak to support a load. "They solved this problem by making the earliest wagons quite narrow, so they could have short axles, which made it possible to have an axle that wasn't very thick," says Anthony. But the real reason it took so long is that whoever invented the wheel would have needed metal tools to chisel fine-fitted holes and axles. "It was the carpentry that probably delayed the invention until 3500 BC or so, because it was only after about 4000 BC that cast copper chisels and gouges became common in the Near East.""