Maintaining the peace is harder on Arth than in many other worlds. Most of the work involving protecting citizens, investigating villainy, and defending property falls to the Heroes’ Guild. And while professional heroes are very good at stopping threats, they are very bad at doing so in a safe or orderly manner.
But someone must keep the peace, and patrol the streets and ramparts, and take down reports when the Elves next door have been throwing raging parties at all hours of the night. For that plodding, every day sort of heroics, duty calls upon the bannermen.