The first wheeled vehicles were likely created by the Sumerians in ancient Mesopotamia (modern-day Iraq) around 3500 BCE. These early vehicles were simple two-wheeled carts pulled by animals, such as oxen or donkeys. The wheels were made of solid wood and the axles were made of wood or leather. Over time, the design of wheeled vehicles would evolve and improve, with innovations such as spoked wheels, metal axles, and suspension systems.