Ancient Tech

The discovery of the Antikythera Device; some ancient high tech that shouldn't exist:

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.