I always thought that there must be like a citizen militia of some sort as well. It would take a lot of serious man power to properly secure the walls around the city and titans are too valuable to be wasted by the thousands just sitting in barracks around the city waiting to repel small raiding parties and scouts. Plus there must be a significant police presence for a city of several million. Seen marks and lore mentioning that some titan orders are brought in on occasion to restore peace and order in the city, but what about the everyday shit? So be nice to see some regular soldiers on Earth at least who look at us with awe like the marines do in Halo to the spartans or like the regulars do to the pilots in titanfall.