Hero of Alexandria(10 — 75)
Hero of Alexandria
8 min read
A Greek engineer and mathematician of the 1st century AD, Hero of Alexandria authored numerous mechanical inventions and foundational mathematical works. He designed the aeolipile, the first device to harness the power of steam, as well as automata and theatrical machines.
Frequently asked questions
Key Facts
- 1st century AD: active in Alexandria under the Roman Empire
- Invented the aeolipile, a sphere set in rotation by steam — the earliest known steam engine
- Designed automata driven by systems of pulleys, ropes, and water for use in theaters
- Wrote the Metrica, a treatise on calculating areas and volumes still in use today (Heron's formula)
- Wrote the Pneumatica and the Mechanica, encyclopedias of the machines of his time
Works & Achievements
A treatise in two books describing more than a hundred mechanical devices powered by air and steam pressure, including the aeolipile. It is the primary source for the study of Hero's machines and a founding milestone in fluid mechanics.
A mathematical work in three books devoted to calculating areas and volumes, containing the famous Hero's formula for the area of a triangle from its three sides. Rediscovered in 1896 in Constantinople, it is still taught in schools today.
An engineering treatise preserved in its Arabic version, covering the five simple machines (lever, wheel, wedge, screw, pulley) and their combinations for lifting loads. The principal engineering manual of Greek antiquity.
A construction manual for theatrical automata describing two types of self-operating mechanical scenes. The first treatise on robotics in history, unmatched in antiquity for its precision and inventiveness.
A surveying treatise describing the construction and use of the dioptra to measure angles, distances, and elevations. It includes a famous problem about tunneling through a mountain from both ends simultaneously.
A treatise on geometric optics studying the properties of flat, concave, and convex mirrors. Hero states the principle that light follows the shortest path, anticipating Fermat's principle by sixteen centuries.
Anecdotes
Hero of Alexandria invented the aeolipile, a metal sphere connected to a boiler by pipes. When the water boiled, steam escaped through two small bent nozzles and made the sphere spin on its axis. This scientific toy, which the Alexandrians admired without grasping its full potential, is considered the world's first steam engine — eighteen centuries before the Industrial Revolution.
To impress temple worshippers, Hero devised an ingenious mechanism: when a priest lit a sacred fire on the outdoor altar, the heat expanded the air inside a sealed vessel, triggered hidden counterweights, and caused the heavy temple doors to slowly swing open. Visitors, unaware of the mechanism, believed they were witnessing a divine miracle.
The “Hero's fountain” is a hydraulic device that seems to defy gravity: water rises on its own in a jet through a system of communicating vessels and differences in air pressure. This invention shows how Hero turned natural phenomena into scientific spectacles, and Hero's fountain is still reproduced in physics classes around the world.
In his treatise the Metrica, Hero demonstrated a formula for calculating the area of a triangle knowing only the lengths of its three sides, without measuring its height. This formula, which still bears his name, is taught in schools around the world more than two thousand years after its discovery.
Hero designed automata for the theater of Alexandria: a small mechanical stage capable of performing an entire play on its own through systems of ropes, counterweights, and toothed wheels. Audiences watched characters move, lightning flash, and ships sail across a simulated sea — all without a single human actor present.
Primary Sources
If a spherical globe is suspended so as to rotate on itself, and two tubes bent in opposite directions are fixed to it pointing toward the ends of the horizontal diameter, steam introduced into the globe will escape through these tubes and cause the device to spin.
Let there be a triangle whose sides measure 7, 8, and 9. Add the three sides together: you get 24. Take half of that: 12. Subtract each side from this semi-perimeter and multiply the remainders together; the square root of the resulting product gives the area.
We shall now describe an automatic theatrical scene: the figures move of their own accord, perform their actions, and the stage closes when the performance is complete — without any human hand intervening during the show.
The five powers by which a weight is moved with lesser force are: the windlass, the lever, the pulley, the wedge, and the endless screw. Each can be understood through the circle, for it is in the nature of the circle that the marvellous resides.
To measure the distance between two inaccessible points, the instrument is positioned so that the line of sight passes through both points; by rotating the graduated disk, the angles are read and the distance is calculated by geometry.
Key Places
City founded by Alexander the Great and the intellectual capital of the Hellenistic and later Roman world, where Heron lived, taught, and conducted most of his research. It was home to the Mouseion and the Great Library, unique centers of ancient science.
A Ptolemaic royal institution funded by the state and the forerunner of the university, where scholars and engineers from across the Mediterranean world were housed and free to pursue their research. It was here that Heron wrote his treatises and taught his students.
A repository of several hundred thousand papyrus scrolls, holding the texts of Archimedes, Euclid, and Ctesibius that Heron drew on directly in his work on mechanics and mathematics.
Capital of the Roman Empire in Heron's time, a city that drove vast construction projects requiring the lifting machines described in the *Mechanica*, thus ensuring the practical spread of Heronian knowledge.
