Wheeled carts

Even with animals in tow, dragging heavy objects on sleds was tough. Rollers could be added to the sledge, but this was still inefficient. Wheels with rollers inside the cart were a game changer.
 3,500 BCE Wheeled carts

Even with animals in tow, dragging heavy objects on sleds was tough. Rollers could be added to the sledge, but this was still inefficient. Wheels with rollers inside the cart were a game changer.