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I messed up. I was writing quickly and confused the Castle with the Tower. (When in a hurry, one's own Tower doesn't help). I was also enlightened about the fortified moat; otherwise, it would just be a trench, a trench (it was truly a mental block).
Here's another interesting point about the Tower. There are no mines, and there can't be any, on cursed lands. This is very bad.
Here's how I won the battle against the Gorgons. The walls were destroyed, the Towers weren't firing, and hoping for champions to attack is pointless – 1 champion against an entire army. The Gorgons don't cross the moat and lose a turn and 1 life. After thinking it over, I cast the Slow spell on the Gorgons, the Haste spell on the champions, and moved them precisely to the opposite side of the walls (i.e., not inside the Castle, but outside). The Gorgon crosses the moat and, hop, loses a life again. We ran around like this for a long time and persistently; the main thing is not to mess up the morale. And here's the trick. It seems simple, but if you just move the champion not exactly opposite the Gorgon, it will cross (go around) through the broken gate without any damage. Here, the unit's speed wins (and my ingenuity, of course). But I got a huge adrenaline rush....