User blog comment:Ktrfgfg/Chapter 53 Predictions + Volume12Special/@comment-6049744-20131213013802/@comment-179280-20131213020959

Well, Historia does not know anything about the Walls, in fact. They need her because she's related by blood to the Reiss family who are able to speak about the secrets of the Walls.

And about Lord Reiss, yes, he may know something, but he's not the Mayor of Stohess. I also suspected he could be, because how they designed him in the Anime, but looking back to Volume 8, they are clearly not the same person.

About the Beast Titan, you can see at the start of Chapter 40 that he leaves the Walls, so, he's in the outside world at the moment, and it's uncertain when will we see him again.