• The wheel and the axle didn't suddenly spring up, but were a gradual, phased invention, starting with rollers that reduced friction on the ground, and helped the Egyptians and Mesopotamians move heavy objects.
• The oldest discovered axle was found inside a potter’s wheel in a miniature, toy-like form in Mesopotamia. The fact that the center of the wheel is stationary as compared to the circumference is in fact the greatest mechanical insight ever known.
• Combining the wheel with an axle was genius, leading to the invention of the wagon and other transport vehicles.

Invention often comes in stages and phases, when existing technology is looked at and mixed with new creative insights, a process that sometimes takes thousands of years.

This makes it hard to pinpoint the exact time and place a certain object is invented.