Colorized engraving shows the details of a steam-driven mechanical apparatus for opening doors. 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. Hero published a description of a steam-powered device called an aeolipile (rocket style jet engine which spins when heated). Among his most famous inventions was a windwheel, constituting the earliest instance of wind harnessing on land. He is said to have been a follower of the Atomists. Atomism is a natural philosophy. They theorized that the natural world consists of two fundamental parts: indivisible atoms and empty void. Much of Hero's original writings and designs have been lost, but some of his works were preserved in Arab manuscripts.