On a certain turn in my game (late game-ish 170 turns i think, expert difficulty iirc)  an ai army of 2 cavalry appears next to my city and attacks it.

I searched the entire area and the army simply wasn't in range.  There's no way it could have walked there.  I tried reloading and same thing happens; if I leave guards in the city, then another city seems to get attacked.

I don't think it's call of the titans as it's only one army that appears; and I can see that he has other armies on the map.

I can't think of any other spell that would allow this; though I may be missing one.

At any rate; it's very frustrating to have an army spontaneously appear in your lands to take a city with no warning or explanation, when you can see ther'es no way they could have gotten close by walking.

You should at least receive a notification if an army appears in your territory by spell so you know how they got in; otherwise it sure looks like a bug; and you'll get more bug reports from people seeing armies that had no way of getting to wehre they got.

Also the ai has no way of seeing which cities are defended; but i'm assuming the ai was given free scouting as ai's are often given.

 further edit:  the ai attack usually happens on season 164, attacking the city next to where abeix was before i killed him.  i've had the entire area near that scouted, and could see no army was within range; but still the army appears and attacks it.

edit, links; also I find it poor form that i can't directly upload bug-related info to here.

http://pastebin.com/hFTC1qmx

http://www.filedropper.com/bug1