Quote from WIKIPEDIA
"The Antikythera mechanism is an ancient artifact believed to be an early clockwork mechanism. It was discovered in a shipwreck off the Greek island of Antikythera, between Kythera and Crete, and has been dated to about 87 BC.
The wreck was discovered in 1900 at a depth of about 40 m (140 ft), and many statues and other works were retrieved from it by sponge divers. On May 17, 1902, archaeologist Spyridon Stais noticed that one of the pieces of rock had a gear wheel embedded in it.
The mechanism is the oldest known surviving geared mechanism, made from bronze in a wooden frame, and has puzzled and intrigued historians of science and technology since its discovery. The most commonly accepted theory of its function is that it was an analog computer designed to track the movements of heavenly objects. Recent working reconstructions of the device support this analysis. The device is all the more impressive for its use of a differential gear, which was previously believed to have been invented in the 16th century"