[roywiggins]

Wheelbarrows relatively simple, you don't need a long axle and, of course, only one wheel. And they are pretty good on poor roads.

http://www.lowtechmagazine.com/2011/12/the-chinese-wheelbarr...

[WalterBright]

Making a spoked wheel is not simple. (Remember, all you have to work with is wood and a stone axe.)

A solid one is easier to make, but will be very heavy and have severe durability problems.

You also have never seen a machine in your life. You have nothing at all to guide or inspire you.

Wheels might have been invented and then abandoned and forgotten multiple times, because they were too hard to make and not that useful.

[pbhjpbhj]

I imagine the model would come from moving things on rollers, out perhaps from turning food on a spit.

From a piece of wood hanging on notched or Y shaped branches on which to hang meat for smoking/cooking to a spit to a pulley doesn't seem to far?

A simple barrow is a couple of sticks with a pulley. Though the utility over a simple dragged carrier is not much.