In the first century AD a Greek inventor known as Hero of Alexandria came up with a new invention that depended more on the mechanical interaction of heat and water. He invented a rocket-like device called an aeolipile, also known as Hero's engine. It used steam for propulsion. Hero mounted a sphere on top of a water kettle. A fire below the kettle turned the water into steam, and the gas traveled through the pipes to the sphere. Two L-shaped tubes on opposite sides of the sphere allowed the gas to escape, and in doing so gave a thrust to the sphere that caused it to rotate. Hero (or Heron) of Alexandria (10-70 AD) was an ancient Greek mathematician and engineer from Alexandria, Roman Egypt. His work is representative of the Hellenistic scientific tradition and he is often called, the greatest experimenter of antiquity.