By Jo Marchant via Smithsonian.com:
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After 2,000 years under the sea, three flat, misshapen pieces of bronze at the National Archaeological Museum in Athens are all shades of green, from emerald to forest. From a distance, they look like rocks with patches of mold. Get closer, though, and the sight is stunning. Crammed inside, obscured by corrosion, are traces of technology that appear utterly modern: gears with neat triangular teeth (just like the inside of a clock) and a ring divided into degrees (like the protractor you used in school). Nothing else like this has ever been discovered from antiquity. Nothing as sophisticated, or even close, appears again for more than a thousand years.
For decades after divers retrieved these scraps from the Antikythera wreck from 1900 to 1901, scholars were unable to make sense of them.