Too early in the game to get a good feel for that - there are literally over a hundred cities I haven't encountered. and nothing showed up in the logs at least.
After a bunch of attempting to read off the logs and see what had happened, I ended up just deleted half a continent. Didn't do a thing, so I deleted the other half.
That allowed me to quickly narrow it down to the Indian civilization. Specifically, not a specific city, but units located within their capital city. Those units comprised of:
Code:
1 trireme
1 war galley
4 galleys
4 light swordsmen
1 pikeman
2 horsemen
1 chariot
2 archers
None with much notable experience. I simply deleted the units, recreated the archers and melee units in the city, and recreated the other units outside the city. Things worked well again.
Except that now I know the Indians have had the money to build up a nice little force of swordmen and naval units.... I haven't had the chance to build any of those after crashing my economy on my takeover of the Roman empire. And they're even more expanded than me. Yipe! That's what I get for a civilization with no happiness resources or econ resources available on my continent...
Oh, and it wasn't a combat. No barbarians in range, no wars involved. Just single internal movement decisions.