My deep gratitude to "Kweklos", the man who was the ceator of the greatest invention ever. (Yes, it was also invented independently halfway across the world, but thousands of years later. And, funny, both inventions were inspired by kids' toys. Toys made by potters.)
Without this man, we wouldn't be riding bicycles.
His invention went so viral that it was a working part of nearly every culture of Asia and Europe withing 300 years! In a day when cultural barriers were like Atlantic oceans. Once you saw just one of these, however briefly, you didn't stop until you had figured out your own.
The wheel. Specifically, the full size wheel and wagon. Very interesting article from "Wired".
I like the idea that it all happened at once; inspired by a kid's toy but the full size end product required: metal tools that could accurately enough create a working wheel to axle fit, wheels had to be designed and made (built from planks pegged together; a simple cross-section of tree trunk would never be strong enough, be very heavy and prone to warp), wheels and axles would have to be sized to both roll easily and not break.
And maybe "Kweklos", the driver found buried on the oldest wagon ever found was that man, his burial starting a tradition that continued for millennia.
The author also speculates that some ancient wagons being spindle and wheel instead of axle and wheel may well have been the result of a long distance sighting with no opportunity to see the details, not proof of independent invention. Of course, we bike riders take advantage of both. Wheels and bottom brackets. So, thank you, thank you.