Before the invention of the wheel in 3500 B.C., humans were severely limited in how much stuff we could transport over land, and how far.
The wheel itself wasn’t the most difficult part of “inventing the wheel.”
When it came time to connect a non-moving platform to that rolling cylinder, things got tricky, according to David Anthony, an emeritus professor of anthropology at Hartwick College.
“The stroke of brilliance was the wheel-and-axle concept,” Anthony previously told Live Science. “But then making it was also difficult.” For instance, the holes at the centre of the wheels and the ends of the fixed axles had to be nearly perfectly round and smooth, he said.
The size of the axle was also a critical factor, as was its snugness inside the hole (not too tight, but not too loose, either).