A wheel is a disc- or circle-shaped mechanical device. Its main purpose is to allow things to roll; in other words, the wheel spins, and object on the wheels moves more easily along the ground. It is a simple machine. Most land vehicles roll on wheels. Wheels are often used in pairs, connected by a rod of wood or metal known as an axle. Many machines have wheels with teeth, known as gears.
Most experts believe that the ancient Mesopotamians invented the wheel about 3500 BC. People in Asia also discovered it on their own around 3500 BC. The Inca and Maya had wheels on children's toys around 1500 BC, but they did not use wheels for work. Africa south of the Sahara desert, Europe, and Australia did not have the wheel until people there met people from other places. Early wheels were solid disks; the spoked wheel was invented around 2000 BC.
The earliest documentation of a vehicle with wheels is a painting dated between 3350-3500 B.C.