Nope. Two or so militia in the city, plus the several archers and/or mages, and only the militia take part in the fight. It happened 3 or four times, and is very frustrating, as the city that was moderately well defended just becomes a rollover for the enemy. Like I said it was a game changer, and annoying enough that I didn't feel like continuing playing after it had happened several times.
I think the pattern was that I had just built one archer or mage the turn before, and both of the archers or mages would up being placed outside the city in the space where newly created units start. The first time it happened I thought I had moved the unit the wrong way, but after three or four times, I realized that couldn't be what happened. I should try to see if I can get a saved game that shows the problem, but it may be hard.
