From the Introduction
A moderately sized wall built from bricks and a water filled moat surround the town, obviously built not so much for defense, but to make sure everyone has to enter the town through its gates and pay their taxes. At the gate you approach a simple wooden bridge spans the moat, easy to remove in the case of an actual attack and just as easy to replace.
The gate where guards and officials stop everyone entering the city to collect taxes and compare them to the latest wanted posters is flanked by two low towers. Their stained glass windows and the lack of arrow slits once again making clear that this is not an engineering masterpiece built to withstand siege warfare but a means to police traffic on the roads entering or leaving the city.