The Antikythera Mechanism

(I bet, you know this one already)
A perplexing artifact was recovered by sponge-divers from a shipwreck in 1900 off the coast of Antikythera, a small island that lies northwest of Crete. The divers brought up from the wreck a great many marble and and bronze statues that had apparently been the ship's cargo. Among the findings was a hunk of corroded bronze that contained some kind of mechanism composed of many gears and wheels. Writing on the case indicated that it was made in 80 B.C., and many experts at first thought it was an astrolabe, an astronomer's tool. An x-ray of the mechanism, however, revealed it to be far more complex, containing a sophisticated system of differential gears. Gearing of this complexity was not known to exist until 1575! It is still unknown who constructed this amazing instrument 2,000 years ago or how the technology was lost.