The Antikythera Mechanism

In 1901, sponge divers exploring a Roman-era shipwreck off the Greek island of Antikythera recovered a corroded lump of bronze that, decades later, turned out to be one of the most sophisticated devices to survive from the ancient world. X-ray and CT imaging eventually revealed more than thirty interlocking gears packed inside a wooden case roughly the size of a shoebox, along with faint Greek inscriptions describing what the device did. Built sometime in the second century BCE, the Antikythera mechanism used its gear trains to track the position of the sun and moon, predict eclipses years in advance, and even model the irregular motion of the moon across the sky. Turning a hand crank on the side advanced the gears in sync, letting the operator dial forward or backward in time to see where the heavens would align on a given date. No comparably intricate geared instrument appears anywhere in the historical record for well over a thousand years afterward, which has left researchers debating how such precision was achieved and why the knowledge behind it seems to have vanished so completely. The device is now generally described as the earliest known analog computer, built not to calculate abstract numbers but to model the sky itself.