All castles in Heroes 3.

Regarding the trench. In the Castle, mines are removed by dispelling them with an expert. It takes away a lot of experience. The worst trench is in the Stronghold. If you stand on a trench near a wall and don't make a move (forward, backward), it seems like health isn't drained. I played in the Lake of Plagues, and a huge army attacked me in the castle. In the end, I had 1 Knight and 30 magic points left, while the enemy had 35 powerful Gorgons and 2 magic points. Question: how did I win the battle?