That reminds me of something that happened to me once.
The AI hates a vacuum.
The Greeks were pounding on Russia (my ally) so I sent some
troops over to help- mind you this was *way* far away from my
homeland. I found I didn't have enough troops to hold a city,
so I'd either take it and trade it to the Russians, or just raze it...
After a while the balance of power in the area was more to my
liking, but there was just one more city I needed to raze. So I
razed the city, pillaged a bunch of improvements (so there were
no roads between Greek and Russian territory) and extorted
some stuff from the Greeks for a peace treaty.
At which point the Greeks sent a settler and every single worker
they had, to rebuild the city and the improvements- escorted
by one single unit. Seeing as I had 6 cavalry still in the area,
I couldn't resist. At the end of it I had 14 captured workers.