Sieges are too difficult at huge scales.
It was 1000 to 2000, we were in a city with full fire catapults, but even though we took out all siege engines, and used every single fire pot by throwing it on them, they still easily broke down the gate with nothing but their weapons. It took a while, but their waves were twice as big every time, so we were overwhelmed. They took pretty huge casualties, but in the end, we lost, and they still had plenty left over after their wounded recovered. I personally killed 75 before I was knocked off the wall. There is nothing you can do. Breaking down the gate with weapons? The main gate? It's actually hopeless. Any helpful tips?