The shoebox-size chunk of bronze didn't attract much attention when divers retrieved it from an ancient shipwreck off the Greek island of Antikythera in 1901. Archaeologists had their hands full with far more impressive finds, including life-size statues of warriors and horses, delicate glass bowls and scores of ceramic vessels called amphorae.
Decades would pass before scientists realized that the nondescript bronze — now called the Antikythera Mechanism — was the biggest treasure of all.
The device consisted of a series of intricate, interlocking gears designed to predict eclipses and calculate the positions of the sun, moon and planets as they swept across the of the sky.
The machine exhibited a level of technological sophistication no one dreamed was possible when it was built, at least 2,000 years ago. Europe produced nothing to equal it until the geared clocks of the Medieval period, more than a thousand years later. Some scholars describe the Antikythera Mechanism as the world's first analog computer.
"The amazing thing is the mechanical engineering aspect," said James Evans, a physicist and science historian at the University of Puget Sound in Tacoma, Wash. He is part of an international group working to crack the puzzle of the device's origins and purpose. Evans recently added a new twist with an analysis that suggests it dates to 205 B.C. — as much as a century earlier than previously believed.
If he's right, it is more likely that the Antikythera Mechanism was inspired by the work of the legendary Greek mathematician Archimedes. It would also mean the device was built at time when scientific traditions from multiple cultures were coming together to create a new view of the cosmos. "Pushing the date back is exciting," Evans said. "We think it would be highly significant because it could change the picture of the development of Greek astronomy."
Scientists think the ship was a merchant vessel that foundered around 60 B.C.
Archaeologists eventually identified more than 80 corroded fragments believed to be part of the Antikythera Mechanism, including the shoebox-size piece with dials and gears clearly visible on the surface.
The real breakthrough came in 2005, when a team of scientists used X-ray tomography to peer through the encrusted metal and reveal the layers of gears inside. Digital techniques yielded the first sharp images of the inscriptions on the dials and casings. The studies revealed at least 30 interlocking gears, and researchers believe the device held at least two dozen more.
The assembly was housed in a wooden box and operated by a hand crank. Elaborate dials traced the movement of heavenly bodies, while gearing mimicked the fluctuating speeds at which the moon crosses the sky, even though the Greeks had no understanding of the elliptical orbit responsible for the effect.
One dial plotted the four-year cycle of Olympic Games. Another predicted the timing of solar and lunar eclipses, apparently down to the hour.
That was the dial that Evans and Christian Carman of the University of Quilmes in Argentina, focused on for their new analysis, published in the Archive for History of Exact Science. Based on the style of Greek lettering on the Antikythera Mechanism, previous estimates of its construction date ranged between 150 and 100 B.C. But Evans and Carman took an astronomical approach, comparing eclipse dates on the mechanism to Babylonian eclipse records and a NASA eclipse catalog.
They concluded that the "start date" for the eclipse predictor was 205 B.C.
That date is tantalizing because it would bring the device closer to the lifetime of Archimedes. The genius who revolutionized geometry and invented compound pulleys was killed in 212 B.C. That means the inventor died seven years before 205 B.C., and there's no way to link him to the Antikythera Mechanism. Evans said, "You would have to think that whoever built this must at least have made use of what Archimedes had done, or came out of a tradition that started with Archimedes."