As per the title, I was wondering if anyone could recommend any books, websites or gaming resources that give details on the kind of fortifications they had in the time period Wolves is based on? Roman forts would also be appreciated. 

Not necessarily looking for battlemaps, just want to have a better grasp of the period.

wikipedia has a pretty good discussion around hillforts - you can extrapolate what some of the cultures of Wolves might have developed on top of that. 
beyond that, a lot of fortifications would likely be a mix of wood and stone, based upon the roman fort model - the low population count makes large stone fortifications very difficult, potentially limiting this to mostly an outer wall.  in a lot of the map, some of the roman fortifications would still be standing. 

Very cool. Thank you for your response (sorry for my late thanks). I keep having to check myself from making to many assumptions over what is and isn't available in the time period this is based off of.

My players ended up joining with Contin and their...interesting religion right away, and planned to burn down Dun Dulnadd.