How did Heron of Alexandria’s automatic devices work?

Heron of Alexandria, a Greek inventor flourishing in the 1st century CE, designed various automatic devices—often described as mechanical toys—that functioned through the application of mechanics and pneumatics.1

These automatons were primarily actuated by three power sources:
* Water: Many devices utilized hydraulic pressure to create movement, such as in water-operated figures or organs.12
* Falling weights: Gravity-driven mechanisms provided consistent energy to operate complex movements.2
* Steam: Heron famously described the aeolipile, an early steam-powered engine where steam escaping from nozzles on a rotating sphere produced motion.1

Detailed in his writings, such as Pneumatica and Automatopoietica, these inventions included singing birds, puppets, and coin-operated machines. By utilizing these physical principles, Heron created seemingly spontaneous movements that were designed to inspire surprise and awe. His work laid a foundation for engineering that influenced later generations, including the revival of interest in mechanical objects during the Renaissance.12