Stop 20 of 109 · Crank to Olympia
c. 150 BCE · Antikythera, Aegean Sea
Inside the 2,000-Year-Old Machine That Predicted Eclipses
A corroded lump pulled from a Greek shipwreck turned out to hide the oldest known geared calculator, accurate enough to track the moon, the Olympics, and solar eclipses decades out.
In 1900, sponge divers off the tiny island of Antikythera found a Roman-era shipwreck scattered with statues, glassware, and coins. Among the wreckage sat an unremarkable lump of corroded bronze, easy to overlook beside marble gods and bronze horses.
It wasn't overlooked for long. Inside were gears: eventually 30 of them, surviving today as 82 separate fragments, one gear alone carrying 223 teeth. Nothing else this intricate survives from the ancient world, and nothing comparable would be built again for well over a thousand years.
Reconstructed, the device is a hand-cranked box. Turning the crank moves pointers tracking the sun and moon, while two spiral scales on the back do more specialized work: one counts the 19-year Metonic cycle of 235 lunar months that keeps a lunar and solar calendar in step, with a smaller dial nested inside it for the four-year cycle of Greek games: Olympia, Nemea, Isthmia, and Pythia. The other spiral, 223 months long, tracks the Saros cycle and marks the timing of eclipses.
Exactly when it was built is still argued, with estimates ranging from about 205 to 87 BCE, but its place as the oldest known geared calculator is widely accepted among historians of science.
The mechanism's gearing, translating one cycle into another, does the same essential job as the moon-phase and calendar complications inside a mechanical watch today. It simply got there two thousand years early.