Has Argos been ceded to you yet? You can't swap tiles until the city is "officially" yours.
I thank you so much for this....
I had a huge army and was waiting till my city finished it's commercial hubto make The Terracotta Army.
I just took over a city that was close to my encampment. The next turn it said that the people of the newly conquered city were starving. So I swapped a tile that had a farm on it which was right next to my encampment because I was waiting 3 more turns for my hub the worker will have repaired a couple farms by then.
So, commercial hub is done, I go to swap the time back and I can't!!!
WTH
I was certain that I knew all the rules about placement, so I search at the screen intensely. Click here, click there, try this, try that, nothing.....Ok google, found this post, saved my sanity, thank you.
I guess I didn't know every thing about placement.