Antikythera Mechanism, Fragment A

The largest surviving piece of the Antikythera mechanism, a bronze gear train from ancient Greece. Look for the four-spoked wheel at the center: it is the main drive wheel, and its corroded teeth still mesh with smaller gears behind it. Turned by hand, the mechanism modeled the movements of the Sun and Moon and predicted eclipses. Sponge divers recovered the fragments from a Roman-era shipwreck off the island of Antikythera in 1901, and they are now in the National Archaeological Museum in Athens.