A chemical analysis of the bones of ancient Nubians shows that they were regularly consuming tetracycline, most likely in their beer. ...

"We tend to associate drugs that cure diseases with modern medicine," Armelagos says. "But it's becoming increasingly clear that this prehistoric population was using empirical evidence to develop therapeutic agents. I have no doubt that they knew what they were doing."
http://www.eurekalert.org/pub_releas...-abm090210.php

I've seen this story around before. It's an interesting one.