Who are the soldiers inside my walls and what are they doing?

There are some soldiers that walk the roads in your city, they are patrolling. It is just an animation to show some life in the city, they don't do anything.

You will also see some animations at your rss production locations. And there are the random 'marauders' that you can tap on to have the dragon destroy them. And also the deer that you can tap to hunt.