The Antikythera clockwork was a mechanical device, made of bronze and iron gears, that was manufactured by the ancient Greeks in the second century B.C. It was lost in a shipwreck around 150 B.C., and recovered from the bottom of the Mediterranean in 1900. But it was only in the last couple of decades, with the help of sophisticated imaging equipment, that scientists have realized what the rusted hunk of metal actually is:
The Antikythera clockwork is a computer. And a very sophisticated and exact one at that.