Originally Posted by HowlerKarma
The Medieval period in Europe, at any rate, is a fascinating time for studying what happened to people like that. There seems to have been a surprising degree of social mobility available given the other constraints inherent in the era.

The entire High Middle Ages was a time of significant social mobility.

One example of the way for a cobbler's son to become Pope.

http://en.wikipedia.org/wiki/Pope_Urban_IV