In 1901, sponge divers working off the Greek island of Antikythera found a shipwreck. Among the statues and pottery was a corroded lump of bronze that nobody could identify.

It took a century to work out what it was: an analog computer, built around 150 to 100 BCE.

Modern X-ray CT imaging revealed the inside. At least 30 bronze gears in a clockwork arrangement, packed into a wooden case about the size of a shoebox. The front dial tracked the sun and moon against the zodiac. The back had two spiral dials — the upper one running the Metonic calendar cycle, the lower one predicting eclipses. A small subsidiary dial inside the Metonic spiral tracked the timing of the pan-Hellenic games, including the Olympics.

The accuracy is what gets me. The main gear ratio of 19:254 captures the Metonic cycle exactly — the nineteen-year period after which the moon’s phases fall on the same dates. Another gear train handles the Saros cycle, the 223 months between similar eclipses. And it accounted for the moon’s elliptical orbit through a pin-and-slot device that varied the display’s speed as the moon sped up and slowed down.

Somebody in the second century BCE understood that the moon doesn’t move at a constant rate, and built a machine to model it.

Here’s the real mystery: it’s alone. Nothing remotely comparable appears in the archaeological record for another thousand years. Classical historians had assumed precision mechanical devices waited for the medieval Islamic world and later European clockmakers.

You do not build something this good on the first try. The gear-cutting precision and the theoretical knowledge behind it imply a whole tradition of similar instruments. None have been found. Inscriptions on the mechanism suggest it may have been made in Syracuse, possibly connected to the school that grew up around Archimedes — but it postdates his death, so we’re looking at the work of mechanics whose entire output has otherwise vanished.

One thing my research keeps hammering home: our archaeological discoveries are a tiny, tiny fraction of what existed. So much has been lost.

This is one of 100 mysteries explored in The Little Black Book of Ancient Mysteries: Enigmas, Puzzles and Artifacts from the Dawn of History.

Get your copy here: https://amzn.to/4pSLpH6