Note: Sadly, this story turned out to be a hoax. Click here for more detail.
Many thanks to my old classmate Collette McNeill for turning me on to this amazing story.
It turns out that a group of French archaeologists made a remarkable discovery while examining a thousand-year-old piece of Pompeiian pottery. While crafting the piece, the artisan placed the pot on a wheel and inscribed a thin, decorative spiral line down the surface of the pot using a sharp stylus. During this process, the stylus vibrated in resonance with ambient sounds in the room... and encoded those sounds into the grooves on the surface of the pot!
The process is exactly analogous to that used to make old-fashioned vinyl record masters, and the subsequent firing of the ceramic preserved these sounds with sufficient fidelity that the potter can be heard talking and laughing with another person in his workshop. The only source I have been able to find is this video (click on Lire la vidéo), recorded from French television. The narrator—one of the French archaeologists—describes the process, after which the viewer is treated to a playback of some of the recorded voices.
It boggles the mind: you are listening the the voice of a man who has been dead for a thousand years. Now that this technique is out there, you have to think it's only a matter of time before we find other accidental audio sources, some of which may fill gaps in the history of civilization from which no written records survive.
I am—assuming that this whole thing isn't just a hoax—utterly blown away.