I'm trying to make a map for shogun 2 where you have to fight between rocks, Some sort of arena. But I can't get it to work.

The spot where I want to fight is seen as mountains which is odd, And sometimes I can't even start the battle and everything is greyed out with alt f4'ing the only option.
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Both problems are shown in the above screenshot. It would be very appreciated if someone could help me fix these annoying and frustrating problems.