Sometime before Easter 1900, Elias Stadiatos, a Greek sponge diver, discovered the wreck of an ancient cargo ship (150-100 BC) off Antikythera island at a depth of 42m. Sponge divers retrieved several statues and other artifacts from the site,
including a mechanical computer designed to calculate astronomical positions.
No earlier geared mechanism of any sort has ever been found. Nothing close to its technological sophistication appears again for well over a millennium, when astronomical clocks appear in medieval Europe.
At the photo below a reconstruction of the mechanism.
More information HERE.