World’s oldest profession ain’t just an expression. :^)
The local population would produce goods and provide services for sale, so as long as the Roman troops were stationed there, the town would thrive. The fact that there is one shows the Romans were there quite a while.
I suspect that such places existed adjacent to all Roman forts, with the likely exception of some of the desert frontier forts, such as this one:
https://freerepublic.com/focus/chat/3836800/posts
The Romans would also provide protection against bandits to the town.
Sort of like pawn shops and small used car lots outside of US military installations?