this city doesn't have walls but i still had to build siege engines in order to attack the city, 8 seconds after deployement fase ( starting battle ) the battle stopped and it told me i lost the battle - i haven't even done anything yet aside from moving my units.
You need to build a ram it's because the engine thinks it's a castle ,so only building ladders or siegetowers while result in the game thinking that you can't get into the settlement because it doesn't have walls.