Tactics for the Swamp (Fortress).

I recently lost to the Swamp faction while playing as the Fortress (lost to another player). Can you give me some advice? Maybe I missed some nuances (I was focusing on archers). Unfortunately, I used all my restarts, and on the third try, the wooden mine was only found on the third week – Champions only appeared around that time. I understood that my opponent was playing a strong faction, but I couldn't imagine how strong! He captured my castle on the second attempt, barely exerting any effort. The number of his units was terrifying, and I couldn't do anything. (I've played against and as the Swamp faction many times. I could win playing as it, but not against it). Is the Fortress, once it gains momentum, truly unstoppable, and is there a way to counter it?
Besides advice and tactics, I'd like to hear real stories about such matches (and not necessarily when playing as the Fortress).