Mind you, whenever a town managed to buy itself a Freiburg status from whatever baron it was originally the fief of, the next two things they invariably did were forming a decent militia (if they didn't have one already - towns and such were required to provide troops as a feudal obligation as well, so there usually was that to build on) and build as good walls as they could afford.
Just in the case the baron, or some other baron, or the next town over trying to do something about competition, tried to mess with the arrangement later.