The Antikythera Mechanism is an ancient artifact discovered circa 1900 CE on a shipwreck known as the Antikythera wreck. The Mechanism is thought to be the world's oldest analog computer yet discovered (dating, scientists think, to the 1st or 2nd century BCE). The Mechanism apparently calculates calendar cycles and positions of celestial bodies using a shockingly intricate system of clockwork-style gears -- though its purpose has been the subject of debate for decades, as gears can be used for lots of stuff. The Mechanism is enormously complex, and analyzing it is difficult because of its age, its condition (we just have a crusty fragment that spent roughly two millennia on the sea floor), and the need to create reconstructions in order to see it operate.

Physical reconstructions have been made -- but now, a video of a virtual reconstruction is available, and I encourage you to take a look (there is no sound, don't adjust your speakers). The video below was created by Mogi Vicentini "based on the theoretical and mechanical model by Michael Wright." (Wright's machine is one of the aforementioned physical reproductions, created by using X-ray tomography.) Check this out, and just think for a moment about how much precision went into creating it -- two thousand frickin' years ago:

(View in higher resolution at YouTube).

For tons more on the Mechanism, check out this Wikipedia entry. Check the References section for lots of additional reading.