The Secret of titans in the Wall?

A cult leader anywhere in the world is a problem. they cause issues similar is the in an attack on titan. here the cult leaders are hiding how the Titans got into the wall. How did Wall become so tall? When I first started watching Attack on Titan I was amazed at how these walls are so big and how did they get there. Humans in an attack on titan can't build such huge size walls it is impossible to build such huge walls so how come they are made.

Well, courtesy of season 2 we got to know little about them. they are made with the crystal similar to the Annie crystal which she got herself covered with. These walls are such strong for that reason. The only person who knew about it was the cult leader. Well played Sir you people are destroying the world already with your agenda leave the anime for the sake of EREN lol joking there.

I Hope this gets resolved in the coming future. This will I am sure the written must have a plan. Tell me in the comments what you guys think about it.