In various magical novels, the main force defending a city is generally not made up of mages.
Even if mages do form the core of the defense, one thing is certainly indispensable: various magical constructs, or to put it another way, all sorts of magical alchemical artifacts.
The world of Hogwarts does indeed belong to a magic-dominated realm, yet even the original Hogwarts world possessed quite a few magical items, such as the Headmistress's joyful spell—the awakening of the stone statues.
Chapter 374