To the left you can see that the town Argos has the Great Wall, and quite far from it to the right I'm attacking Copenhagen. Both of these are controlled by Greece at the moment.
How come my soldiers, two musketmen and two longbowmen, only can move one tile within Copenhagen's borders? I know that the Great Wall often eclipses nearby territory belonging to other cities, but in this case it is clearly outside the wall. I also know that it can be a bit iffy with the graphics, so I reloaded the savegame and there's no wall nearby Copenhagen.