Antikythera mechanism

Sponge divers found this corroded bronze device in a shipwreck off the Greek island of Antikythera in 1901. At least 30 of its interlocking gears survive. They modelled the motions of the Sun and Moon and predicted eclipses, and nothing as complex is known again for well over a thousand years.

Experts still debate exactly when it was made, with estimates running from the 2nd to the 1st century BCE. Calling it a computer means an analog calculator, not an electronic one.