Attack On Titan Manga [Chapter 37] [Chapter 38]
You know that part after the female titan part where suddenly Titans were spotted, Mike died and the survey corps horse rid along the wall to find a hole (which wasn‘t there but they couldn‘t have known)? They themselves knew that it was very dangerous because of course they suspected that there were lots of titans coming through the hole and if they found the hole they needed to flee or fight.
But why didn‘t they just run on top of the wall to find the hole? Of course they can‘t see it but they could see the titans and where they are heading to (to the hole) and they could see the titans going though the hole without risking their lives. I know that Ymir and Historia etc. didn‘t have their gear but Nanaba for example did and she could have helped them get on top of the wall. They even expected there to be lots of titans and the wall is 50 meters high they could see very far. I think it‘s an easier and safer solution.