An aeolipile, aeolipyle, or eolipile, also known as a Hero's engine, is a simple, bladeless radial steam turbine which spins when the central water container is heated. Torque is produced by steam jets exiting the turbine. The Greek-Egyptian mathematician and engineer Hero of Alexandria described the device in the 1st century CE, and many sources give him the credit for its invention. However, at least one source credits Vitruvius as the first to describe this appliance in his De architectura.