Is it impossible to build railroads inside a city square after founding the city? By city square, I mean the square occupied by the city icon.
Example:
(Case 1) After gaining the railroad advancement, when you found a city on an unimproved grassland tile, the city is founded with that square irrigated and with a road. When you try to build railroads inside the city square after that, you cannot.
(Case 2) After gaining the railroad advancement, you build roads then railroad on a grassland tile, then found a city on that tile. That city is founded with that square irrigated and with a railroad.
The same seems to hold for fortresses.
Example:
(Case 1) After gaining the railroad advancement, when you found a city on an unimproved grassland tile, the city is founded with that square irrigated and with a road. When you try to build railroads inside the city square after that, you cannot.
(Case 2) After gaining the railroad advancement, you build roads then railroad on a grassland tile, then found a city on that tile. That city is founded with that square irrigated and with a railroad.
The same seems to hold for fortresses.