In 1900, Elias Stadiatos was diving near the Greek island of Antikythera searching for sea sponges when he encountered what appeared to be a pile of dead, naked women on the ocean floor. Distressed, he surfaced an informed others of his find, and a closer inspection was made of the area. Elias's "dead women" were in fact ancient statues lying in the midst of a Greek ship which had sunk there around 87 BC. The statues had been part of its luxurious cargo, which also included jewelry, pottery, fine furniture, and wine. The sponge divers brought up as many interesting objects as they could manage, producing an orgy of artifacts.
About two years later, on May 17, 1902, an archaeologist named Spyridon Stais was examining some of the pieces, and noticed a chunk of green rock which had a gear wheel embedded within it. This gear was the first evidence of an ancient Greek computer which would come to be known as the Antikythera mechanism. Technology in the early 1900s did not allow for peering into the rock further, but it was clear that this was the oldest gear-driven mechanism ever to be discovered.
It would be almost sixty years before a science historian at Yale University named Derek J. de Solla Price suggested that this might be one of the celestial-body tracking instruments described in several ancient Greek texts. Experts balked, as some are wont to do, because it was generally thought that such stories were fictional, and that the ancient Greeks lacked the practical skills and technology to construct such an intricate computing mechanism. Gamma ray imaging was employed in the early seventies, and its findings backed up the theory, but the new analysis was met with similar doubt. But more recently, several working replicas of the device have been made which demonstrate that such a clockwork device could have predicted the movements of the sun, moon, stars, and planets with quite a bit of accuracy.
From the Economist article:
The Antikythera mechanism, as it is now known, was originally housed in a wooden box about the size of a shoebox, with dials on the outside and a complex assembly of bronze gear wheels within. X-ray photographs of the fragments, in which around 30 separate gears can be distinguished, led the late Derek Price, a science historian at Yale University, to conclude that the device was an astronomical computer capable of predicting the positions of the sun and moon in the zodiac on any given date. A new analysis, though, suggests that the device was cleverer than Price thought, and reinforces the evidence for his theory of an ancient Greek tradition of complex mechanical technology.
Article on the Economist