I left my Norse cities deserted in the early game seeing as how there were no barbs in Scandinavia (as long as you don't count the vikings themselves ). To my surprise I got a message that Stockholm had been captured and I instantly thought "WTF? When did the Sami arrive? And when did they start capturing viking towns?" I sent the nearest worker to investigate, only to discover it had been conquered by a barbarian wolf! I suppose it's not an unrealistic bug, though - the Nordic archipelago of Svalbard frequently has polar bear incursions in its settlements, and citizens are required to carry rifles outside of town to defend themselves in case of ursine assault.