I'd appreciate some enlightenment on this too - a city that I thought would be moderately well-defended was attacked and recaptured by Gilden because the militia (it was a level 2 city, so would have had three units of militia and one of archers) didn't show, leaving just three units of slaves to fight the invaders.
Was it because of unrest, or because I hadn't held the city long enough? Another city I had captured from Pariden some time earlier was attacked a few turns before and had a full complement of defenders.