How is this possible!!??!?!?!?!?!?!

I play lord of the rings map mordor I am barad dur it's in an "indent" in the mountains, so first turn I made a wall using 2 units, completely sealing it off )))
And the very next turn barad dur is captured!??!?!?! The wall is intact, and I don't think there were even any enemy units around there!!!

!?!?!?!

There are secret paths.

0.o
Where!? How!?

:skull: