There's an advantage at being in the open - you can see and hear the titans coming from a distance. Some of them are fast, but most of them barely have the intelligence of an animal. [Most of them.]

Horses are faster. It's not perfect, but it's the best way to cover distance in titan territory.

[Armin looks out over the buildings. It's hard to see how any of this knowledge could apply to the current situation, but he's working on figuring it out.]

You're asking a lot of questions about this. It doesn't bother me, but why is it of interest?