The Bronze Computer From a Roman Shipwreck

In 1900, Captain Dimitrios Kontos and a team of sponge divers from the Aegean island of Symi were sheltering from a storm off the small island of Antikythera when they spotted a Roman shipwreck 45 metres down. Over the next year, divers raised marble statues, bronze figures, glassware — and one corroded lump of metal that didn't seem to belong with any of it.

The lump went to the National Archaeological Museum in Athens. On 17 May 1902, the archaeologist Valerios Stais noticed something poking out of it: a gear. Greek bronze, about 2,100 years old, with cleanly cut teeth.

For decades, no one knew what it was. The view was that ancient gear-trains of this complexity were impossible. Geared astronomical clocks were not supposed to appear until the 14th century. A few researchers argued the object had fallen onto the wreck later, from a passing ship.

High-resolution 3-D microfocus tomography, applied to the fragments by Tony Freeth and his team in the early 2000s, settled it. Inside the wooden case were at least 30 surviving bronze gears, arranged to predict the positions of the Sun and Moon, eclipses on the 18.2-year Saros cycle, the 19-year Metonic calendar cycle used to keep months in step with seasons, and — engraved on a small dial — the four-year cycle of the Panhellenic Games.

Freeth's 2006 Nature paper is the moment the Antikythera mechanism stopped being a mystery and became a working schematic. Nothing of comparable complexity is known to have existed in Europe for the next thousand years.