In my opinion it shouldn't grant extra turn, as it is not expanding the road, just ending it, similar like it works with the Abbey.
What expansion includes "city gates"?
Only expansion which add road length one I know is Tunnel II 2015 which allow to place tunnel token to magic portal which is automatically close road on that side of tunnel and counter as road length 1..
Started by DrMeeple
Started by coldhands
Started by Yashin-n
Started by Decar
Started by MrNumbers