Citywalls dividing quarters are supposed to be 2m lower than the main citywall.
Well, I have just did that and i can now place it where it belong and by the way fir all buildings near it the way they look good and eveeyting fits.
If i first placed citywall, then some major structures, main road and tried to fill the remaining with premade buildings, I'd probably have problems filling that space in a nice way and instead end up with lots of unused space, what wouldn't look alright in a city where every m
2 matters as everyone want to build within the citywalls and not outside.

We are closer every day.