Neglected defense maybe? 22 zombies isn't that bad really. You definitely want to set up a solid defense anyway, both with units fortified in the ccity, clearing of adjacent forests, and ideally a forward point defense group with roads maybe a fort, good river location and desert, tundra, or grassland ambush tile. Mounted units work great obviously, but I usually just get by with archers for a bit. Sorry if I missed the point of your question though, 22 zombies doesn't sound like a lot to me, and isn't very hard to defend against. Maybe without much happiness and no hills your production was abysmal? Even then with a pagan temple and maybe god king you should still be able to pump out a decent, or at least working, defensive force in a reasonable amount of time.