Perhaps the better way to phrase this is, “Hamsters now work inside person wheels,” because the person wheel definitely came first. These comic-looking but useful devices helped build many of the landmarks we now cherish.
The treadwheel crane first made its appearance in Rome in 25 BC. It flourished with the Roman Empire, and could lift up to six thousand kilograms, but fell into disuse as the empire disintegrated. After the end of the empire, it took roughly a thousand years for the crane to come back into use, and another hundred for the technology to spread through Europe. It was only in the 1300s that these human hamster wheels became common again.
Treadwheel cranes involved two wheels around a single axle, a person in each wheel providing balanced force. As the people walked, they turned a central crank. The crank would reel in a length of rope and haul in whatever was on the end of the rope, the same way you haul in whatever is at the end of a fishing line by turning turning the handle.
The wheels could be set up on top of any structure. Some were built on top of cathedrals and used to haul blocks of stone up the sheer walls. Today, you’re most likely to see recreations of these wheels near rivers or ports. Treadwheel cranes provided efficient ways of getting cargo from a boat onto a dock.
This design was used by laborers. Prisoners also worked on these cranes, but they tended to walk on the outside of the wheel. Inside or outside, the job was dangerous. There was no actual brake on the wheel, although usually workers kept a stick on hand to jam in the wheel.
Still, there must have been instances when an overly-heavy load reversed the motion of the wheel and flattened the walkers to the sides of the wheel as it went crashing back down.
[Sources: Treadwheel Crane.]