HERE is the dropbox save from several turns (2 I think) prior to the above screenshots.  I just replayed from this save and by just hitting 'end turn' I got the same results as describe above (a stack of 11 units hit my city on turn Summer 197 A.D.).  I did see a 'flickering' of the stack of armies on the square below the Air Shard so that seems to be on the 'route' they used.

It's possible due to the vagaries of the RNG that a replay may show different results (tho I saw the same results just now).  If so, perhaps retrying would show my above results.  At the least, this should show where the 11 attacking armies are currently and help explain how they hit me.

Thanks for the help! 

I think that if the AI armies started just on the other side of Stoneham (or within ~3 road tiles of Stoneham), armies with 4 movement could pass through Stoneham as 1 move and take three more to hit your city (I allowed the 3 road tiles because as long as you have a fraction of a movement point you can still enter a tile, which is enough for triggering an attack).

I am a bit surprised, regardless, because at minimum this indicates either a Mancer blood enemy with an army mounted entirely on Wargs or Horses, or a non-Mancer army with an entire army mounted on horses; neither of these cases is something I can recall seeing for full armies, and certainly not for 11 armies.

Also, out of curiosity - is it a single army of 11 units, or 11 separate army stacks that hit your city? And if you play it out, do you see City Militia or anything like that in the army? Also, if you play out the battle, how much of the enemy army is mounted?

Edit: And Parrotmath beat me, and with a better response.

Thank you both for the help! 

Addressing some questions/points:

-there are 11 AI armies in that stack attacking my city, each AI army comprised of 9 units (so 99 units total).  Looking thru all 11 armies (99 units) I saw a total of 4 'city' militia type units, 3 mounted units, 1 pioneer, and 1 scout.

What's curious to me is that my 'scouting' undead stack that I summoned inside the AI territory in screenshot 3 shows no sign of the army stack.  Assuming the stack of armies has 2 movement, and starts near enough their city Stoneham that the army stack can pass thru and exit Stoneham with 2 move remaining (because 3 or fewer movement doesn't 'count') then:

-exit Stoneham in a tile 1 west of the Air Shard (0 moves used, 2 remaining)

-enter tile on Air Shard column (1 move used, 1 move remaining)

-enter tile column 1 east of Air Shard (2 moves used, 0 remaining) and stack is next to my city but no movement left to attack that turn.

Would the army stack exit Stoneham to the Air Shard column instead?  That would allow an attack this turn.

I've lost this game, I lost the city and with no good prospects for new cities I'm toast.  Knowing what's coming (which is cheating of course) there's a chance I could do a few things to delay his approaching armies (Haunted Army spell) then Tornado the stack (or stacks as a couple of times he's split the stack into 2 stacks) then try to mop up.  I'm hoping that AI armies now reform (they didn't a few versions ago) and if so this would only delay the inevitable (and drain most of my mana).

It's heartening to see the AI this effective.  If it continues I'll have to drop down several difficulty levels, to my more usual level of (in)competance lol

Sometimes when you see stuff cheats are worth enabling. I was playing primals game the other day and his sov was swimming. I'm not sure what mods he had. But when you see odd stuff like that it's worth looking at. 

I actually would like a replay feature added to the game, in the way distant future. In Starcraft I generally try to review all my matches. Sometimes after reviewing my games I realize that my opponent didn't cheat, which I assume everytime I loose, but I was just being slow at responding to the game. It's a good way to improve my game play. 

Actually this wasn't cheating since you already had encountered it and knew from that point you lost the game. So, what you were doing is salvaging what you could from the game, which I say is not likely a win scenario.

Call of Titans would do the trick, put the army right on top of the air shard and boom... the stack of 11 I pointed out would be on your city in 1 turn... sad news.

..... I'd love to drop a falling star on that stack of 11 armies

It'd probably obliterate 3/4 of them in first turn then kill the rest next turn and you can take the city back with a single skelly provided taht you have enough fire shards to amplify the falling star's power that much.

I'm curious though, what difficulty are you playing on?

If anyone wants a save of the starting position (before any moving/etc.) I can provide it.

N/A