Yesterday io9 carried a fantastic story on the Antikythera machine, a bit of ancient tech that's becoming more and more interesting:
In 1900, some divers found the wreck of a Roman vessel off the Greek island of Antikythera. Among the other treasures remanded to the Greek government was an unassuming corroded lump. Some time later, the lump fell apart, revealing a damaged machine of unknown purpose, with some large gears and many smaller cogs, plus a few engraved words in Greek. Early studies suggested it was some type of astronomical time-keeping device . . .
But that was just the start. New x-ray scans and 3D models have shown that the Antikythera was more--much more:
Using nothing but an ingenious system of gears, the mechanism could be used to predict the month, day and hour of an eclipse, and even accounted for leap years. It could also predict the positions of the sun and moon against the zodiac, and has a gear train that turns a black and white stone to show the moon's phase on a given date. It is possible that it could also show the astronomical positions of the planets known to the ancients: Mercury, Venus, Mars, Jupiter and Saturn.
All of this was accomplished by turning a crank on the side of the box. And this thing was built around 150 years before Christ. And that's just the starting point:
The true genius of the mechanism goes beyond even the complex calculations and craftsmanship of a mechanical calendar. For example, the ancients didn't know that the moon has an elliptical orbit, so they didn't know why it sometimes slowed or sped up as it moved through the zodiac. The mechanism's creator used epicyclic gears, also known as planetary gears, with a "pin-and-slot" mechanism that mimicked this apparent shifting in the moon's movement.
Like Stonehenge, the Antikythera is one of those things that just shouldn't exist. If you're interested, Scientific American has video and HP has some beautiful shots of the device.